Hmmm. Upgraded to Win 7 Ultimate on my Latitude E6400 last week - have downloaded all updates - no problems thus far. In fact I love it, Win 7 is MUCH cleaner than Vista.
Got a new ASUS a few weeks ago with Windows 7 on it. So far it seems pretty stable.
Usual stupid interface changes MS makes so you have to learn all over how to do basic stuff.
First thing I do with Windows is turn OFF automatic updates. I don’t do patches and updates until everyone else has been using them for at least 6 months. And if my machine is running well, I don’t do them.