Hi all. Just wanted to report the same problem on my Powerbook (15", 1.5 GHz). After updating to 10.4.3 I've been experiencing the same keyboard behaviour you're describing. First key press doesn't register, then the second one does. I hadn't linked it to sleep issues, but it does seem to occur after a certain duration of inactivity. We could probably time it; I'll bet it's the same duration for everyone. I don't have any special energy saver settings (normal for battery, set to 'never' when running on AC power) and I don't require a screensaver password. I sent a short write-up to MacFixit a week or so ago, and it was part of their troubleshooting report but there was no solution. I'll try submitting the bug to Apple.