Both Firefox and Thunderbird have instituted automatic software update features whereby the browser and email reader periodically check their home sites to download any updates. This is a good thing, in my opinion.
However, both programs has also gotten into the habit of popping up a message box, the moment the download is complete, asking "Hey, new updates are here. You need to restart?" And I can choose either "Now" or "Later."
This is annoying. Just think about it: I've been using the old version of your product for months, and things are just fine. And I start and quit Firefox and Thunderbird all the time, at least several times a day. (With Firefox routinely taking up 200M of memory, and not to mention the AJaX induced CPU load, nowadays, I have to close it down from time to time.) Can the newly downloaded stuff wait quietly for just a few more hours for one of my restarts?
And what if I accidentally clicked on the "Now" button? I'd loose my "place"—all the tabs I have opened, and the form I'm in the middle of filling out will be gone. That'll make me very angry. Enough to write a blog entry bashing your feature.