If it's what I'm thinking of, then it's an annoying one. I have it too.
Occasionally the MBP keyboard will miss/ignore the first letter you type if there is a big enough pause beforehand. This is even if you have the energy settings turned to max performance so it doesn't go on standby and the hard drive keeps stays on 100% of the time.
I have this problem, but another keyboard issue is where the keyboard locks up and is just not responsive to any key press for about 1 minute. I also have this issue and have done since I upgraded to Leopard, however, it seems to have got much worse since I installed this Security Update - really hope Apple release a fix soon!