When I use the keyboard to type emails etc I frequently find that it misses letters that I know I've typed. I I'm not a super fast fast typer,so that's no the problem

SOURCE: it's like my keyboard is high.

I had exactly the same problem with a Acer Travelmate last year, from the day I bought it. Eventually I found some kind of fix (maybe it was a BIOS update) from Acer and it has worked perfectly ever since. Sorry I can't remember exactly what, but you may want to go to Acer support web site and just update all your drivers.

I have two co-workers suffering sith the same problem on Acer notebooks and we are trying to hunt down the fix. If you Google Acer keyboard lag, you will find many reports of similar problems.

SOURCE: Dell Inspiron 1300 Keyboard Lag

There is a program that is bundled with Dell machines called the Dell Media Experience. It runs on startup and has been known to cause issues with keyboards and typing speeds etc..... I found that by turning this off via MSConfig the problems associated with my keyboard went away.
Hope this helps.
Start - Run - MSconfig - Start up - Untick PCMService. O.K and restart.

SOURCE: gateway model md7818u keys dont register the letter when struck- happens frequently, especially on the qwerty line

Replace the keyboard -- it's not worth paying a technician to diagnose the problem, and there's little that (s)he can do to repair it.

SOURCE: The keyboard on my Asus M51V series notebook does

I have the same laptop and it does exactly the same thing misses key hits and when i use mine and press a key it doesn't go fully in if you hit the key (very annoying when doing an essay) i find it good just to go over what you typed just to check it. Or get it fixed at a local computer shop, im not really that much help sorry.

SOURCE: Hi, I have a Lenovo

It seems the problem of setting in your applications.