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.
Lookup
macbook pro first key on Google and you'll see what I mean. There's even a ticket logged with Apple. I don't know which revisions are affected, but I know at the very least the LED screen 15" has it (that's mine).
I have the problem and it's really annoying, especially when I'm writing code or have to type in a password. If the machine is idle for a few minutes, chances are your next keystroke will be lost.
The last time I checked, there was no true fix and I believe it even happens with an external USB keyboard. I've heard that the USB hardware might be the culprit because the built-in keyboard might be hooked up to it too. But I've heard lots of theories so take that with a grain of salt.
However I've started using the Bluetooth keyboard to get around the problem. Programming is complicated enough; not but if a numeric constant is typed in wrong it can be killer to trace and debug.
It's kind of disappointing. The last Apple product I had was a 1.25GHz Al Powerbook and it was fine. But this is an annoying enough bug to sour the taste in my mouth a little, especially since its' been ongoing for over 6 months. Sure the Bluetooth keyboard gets around the problem, but when I need to use the MacBook Pro away from the desk I have to be extra careful as I type.