This thing happens to me a lot in Nexuiz, but no other FPS' I've tried. At first I thought it could be ping related, but then I noticed it happens in single player bot matches too.
For a few seconds at a time the keyboard and mouse locks up, continuing doing what was last done before they locked (if I was moving forward or strafing, it keeps on doing so, and if I was firing the gun keeps firing) ... which often leads to bad things like me running and firing a rocket, controls lock up, I continue running, hit a wall and the rocket launcher fires again killing me. I can't seem to find any special circumstances this happens in. I've set all graphic options to the lowest setting, diabled just about all effects, set particles to 0.1 and all that, and it keeps happening.
My computer isn't of the latest model, but should be able to handle Nexuiz fine; it is a AMD Athlon 2600+ 1.92Ghz, 512MB RAM, Asus GeForce N6200, Windows XP SP2 (and a E-mu 0404 sound card, if that would matter).
Another thing that happens to me a lot is that I respawn without HUD, visible weapon and the camera at ground level, as if I was dead. But as far as I could tell others had already reported the same problem in other threads.
I could try to upload a demo somewhere if it is needed.