On this installation of Vista, I've had zero problems with the updates.
As a matter of fact, they only made it all better!
(Fixing some compatibility issues and such)
Previously, however, I have had some problems... Mainly Vista simply
being completely unable to apply some of the updates, sometimes
resulting in numerous consecutive reboots. And when it finally finished
all the rebooting, a little message said "The updates couldn't be applied",
or something along the lines of that. I ended up disabling it altogether.
Then Vista somehow screwed up, forcing me through a long
re-installation process... But ever since, I've had no problems with the updater.
I did disable the automatic installation though, it's really frackin annoying
when the PC reboots without warning while you're doing something >_>
Never had it cut off my internet though.