Wow. Usually, as a techie, I feel it is my job to find the "why" something stops working, instead of just "fix it". Tonight, my Windows Key + Tab wasn't working to rotate through Windows. After some online research, I discovered the root cause was that Aero wasn't functioning on my recent Windows 7 install. After much online research, I simply couldn't figure out why it wasn't on. Finally, I gave up, probably the first time in several years, and reached out to the Windows troubleshooting application.
It seems my desktop manager had been disabled by one of the utility installs I was testing out. I've been looking for a new grid management utility for Window placement. While I still haven't found a nice fit, I am glad to have my Windows 7 functionality working again.