I'm at my parents', and long story short, my laptop has suddenly decided to start locking up anytime Steam comes on the scene.
The only thing that's happened is, I put Steam on my parents' computer so that I could show PvZ to my nephew, and of course the next time I went back to my laptop, Steam notified me that I had been logged out since I had logged in at another computer. I dismissed the message, did some work on the laptop, and shut down the system. The next time I booted up, the system froze at startup, and I finally figured out it was happening when Steam tried to start.
Uninstalled Steam, then reinstalled...and sure enough, at the point in the install process where it would ordinarily start the client, frozen again. And by "frozen," I mean everything...no keyboard, no mouse, nothing to do but a hard reboot.
Any thoughts as to what might be going on with my system that it suddenly doesn't like Steam? By the way, as part of the process of narrowing the problem down, I have already done a system restore to a point earlier in the day (before I installed Steam on my parents' computer). I may try another even earlier point here in a few minutes, though it doesn't seem like that would make much difference, as it was working fine at the time I restored to.
Edit: An additional puzzle piece: I am able to start Steam in Safe Mode (with networking).
Edit 2: Some Google searching brings up some similar tech help threads--none newer than October of 2010--in the problem was the Creative Labs software installed on ASUS laptops, which I have. I'll uninstall that and give it a shot in a few minutes--though I'd be curious to know why I've experienced no issues in the year plus I've owned the laptop, and suddenly, right after a seemingly minor incident involving Steam, the CL software has decided to give me this problem.