I installed this on my 2.2 GHz MBP a few minutes ago. I already saw the problem, still, while working in Excel. Maybe that means this doesn't fix it, maybe it means my problem is with Excel, but it did only start after I went to 10.5.
My temporary fix has been, and unfortunately may have to remain, pressing control and then the right and left arrow keys (kb shortcut for switching between Spaces)-- for some reason, these keys usually aren't affected, and switching to Space #2 brings the kb back to life in Space 1. Command-tab, for example, doesn't work, but control and the arrow keys do! It's weird, I've tried control with other keys, only this combo seems to work.
I've also experienced the dead kb problem on a Core Duo MBP, in Firefox, haven't tested that yet.