Shooting Speed Dropped

It is the buffer count for how many pics you can shoot in continuous mode.
Shooting in different formats (RAW, or Jpeg & sizes) affects the number.
Using a fast card also helps to speed up clear the buffer allowing you to shoot more frames at maximum speed.
Reading The Fine Manual is very helpful for queries such as these.

Set your camera to high speed continuous shooting, track the action, and just before the peak press and hold the shutter release button. The camera will take a series of pictures and hopefully one of them will catch the action at its peak.
If you're asking how to set the camera for high speed continuous shooting, Turn the mode dial to SCN, press the FUNC/SET button, select the overlapping rectangles, and press the DISP button. Full details are in the "High-Speed Continuous Shooting" section of the manual (page 74 in my copy). If you need a manual you may download one here.

Although a good SD card is worth considering it's not the only thing that determines the speed. In fact the shooting light has more to do with it then the memory card. The Rebels although not Pro cameras are pretty darn fast with the differences immeasurable in most cases with Pro cameras.
The Rebel will show the burst rate in the right corner of the viewfinder and if you noticed this rate changes with the light and shutter speeds. Sow the shutter speed down and that burst rate will drop as well. The size of the image file also dictates how fast you can burst in frames per second. You are shooting RAW and no doubt jpg's so the camera is doing double duty with some pretty impressive files size. If you want speed shoot jpg's and set your camera correctly for white balance, shoot for the end use. If you are looking for speed you aren't shooting portraits or landscapes where you have time to calculate your shot so the need for a BIG print isn't necessary so drop your image quality.
The Rebel's processor is very impressive and it has a large buffer where it writes the file as you are shooting so in fact the camera is writing to the buffer at the same time it's writing to the memory card. That's why when you stop shooting it takes several seconds for the camera to catch up.

If you are looking for speed keep your shutter speed up, reduce the image file size, shoot jpg, class 6 works nice (I use this type) I have only one class 8.

On a personal note the Canon Digital Rebel has put so much power and performance in the hands of entry level photographers and they are using that power to come up with some darn nice photography and in the right hands it's putting the hurt to some long time pro shooters.

HI.
Have you been taking pictures continuously?
As in continuous mode you can only capture about 7 raw files before the buffer is full and the shooting speed drops off a cliff.
You can this error message to indicates that your card is full and that influence the shooting speed.

Your cards writing speed may be too slow to continue shooting past 30 sec. You should be using, at a minimum, a class 6 card.

i think the frame rate is 1.3 frames per second.

Issue: How do I set Continuous Shooting?
Solution: Setting Continuous Shooting mode PowerShot SD750 and SD1000.

Continuous Shooting In this mode, the camera shoots continuously while the shutter button is held down. Recording ceases when the shutter button is released. In addition, under the following conditions, continuous shooting can occur at a consistent interval until the SD card is full*.

• A resolution and compression combination other than and is selected.
  * If continuous shooting suddenly stops, the SD card may be full.

Continuous shooting is available in all modes except [AUTO], [Stitch Assist], [Color Accent] and [Color Swap].
To set Continuous Shooting

1. Press the button to display .
   
   
   
2. Shoot the image.
   
   The camera will continue to record successive images while the shutter button is fully pressed. Recording will cease when the shutter button is released, the card is full or the card does not support a write speed to allow continuous shooting to continue.

To Cancel Continuous Shooting

1. Press the button twice to display .
   

To enhance the continuous shooting performance when you suspect the speed has dropped, you are recommended to format the SD card in the camera (Low Level Format) after you save all its images to your computer.

• The interval between shots may lengthen slightly when the camera's built-in memory fills.
• If the flash is firing, the interval between shots will lengthen to accommodate the flash's charging requirements.

must be something to do with the mode you are using like auto mode, manual mode P mode so on...havn't use anything else the the manual mode so do a hit and trial procedure. Also be sure to increase the shutter speed...

There are four sequential modes: Sequential shooting, High-speed Sequential shooting, AF Sequential shooting and Auto Bracketing. Sequential shooting modes can be selected from the CAMERA menu: Sequential shooting: A maximum of 11 frames can be shot sequentially at approximately 1.7 fps in HQ mode. Focus, Brightness (exposure) and White Balance are locked at the first frame. High-speed Sequential shooting: A maximum of 4 frames can be shot sequentially at approximately 3.3 fps. Focus, Brightness (exposure) and White Balance are locked at the first frame. AF Sequential shooting: Focus is individually locked for each frame. The AF Sequential shooting speed is slower than for normal sequential shooting. Auto Bracketing: When Auto bracketing is set, exposure is changed automatically for each frame when you start shooting. The exposure differential can be selected in the menus. Focus and white balance are locked at the first frame.

There are four modes: Sequential shooting, High-speed Sequential shooting, AF Sequential shooting and Auto Bracketing. Sequential shooting modes can be selected from the DRIVE mode menu: Sequential shooting: A maximum of 11 frames can be shot sequentially at approximately 1.7 fps in HQ mode. Focus, Brightness (exposure) and White Balance are locked at the first frame. High-speed Sequential shooting: A maximum of 4 frames can be shot sequentially at approximately 3.3 fps. Focus, Brightness (exposure) and White Balance are locked at the first frame. AF Sequential shooting: Focus is individually locked for each frame. The AF Sequential shooting speed is slower than for normal sequential shooting. Auto Bracketing: When Auto bracketing is set, exposure is changed automatically for each frame when you start shooting. The exposure differential can be selected in the menus. Focus and white balance are locked at the first frame.

There are four modes: Sequential shooting, High-speed Sequential shooting, AF Sequential shooting and Auto Bracketing. Sequential shooting modes can be selected from the DRIVE mode menu: - Sequential shooting: A maximum of 11 frames can be shot sequentially at approximately 1.7 fps in HQ mode. Focus, Brightness (exposure) and White Balance are locked at the first frame. - High-speed Sequential shooting: A maximum of 4 frames can be shot sequentially at approximately 3.3 fps. Focus, Brightness (exposure) and White Balance are locked at the first frame. - AF Sequential shooting: Focus is individually locked for each frame. The AF Sequential shooting speed is slower than for normal sequential shooting. - Auto Bracketing: When Auto bracketing is set, exposure is changed automatically for each frame when you start shooting. The exposure differential can be selected in the menus. Focus and white balance are locked at the first frame.