I installed Windows 7 on a machine at the weekend and I am sadly disappointed by the lack of stability. After a random period of time (sometimes several hours) explorer starts crashing and although it nicely restarts itself, it keeps doing this every minute or two. This issue was apparent on a fresh install with only windows installed.
I have no idea what "starts" this behaviour but once it has started, doing things like right-clicking somewhere, sorting columns in an explorer window or trying to launch the control panel all seem to regularly trigger a crash.
There are many, many reports of similar behavior on Google (the fairly specific search string "windows 7 64 bit explorer crash" brings up over 540,000 results) and many suggested 'solutions' but nothing definite.
Kinda makes me wish I had stuck with XP for a bit longer!