I have a spare MacBook Pro that I turn on twice a month or so. Every time it starts up, I see Google Update asking me to confirm installation of updates. If I click Cancel, it will ask me later.

Firefox updates on start up may be bad, but Sparkle handles this better -- it asks me to update the app I'm using, and downloads it in background.

By the way, Google's update framework for Mac has been there for a few months: http://code.google.com/p/update-engine/. But -- please -- don't use it.