Lemme add a bit to what autocrosser says.
Its never a good idea to just pull updates. What I usually do is do
$ sudo aptitude update
and then do
$ sudo aptitude safe-upgrade
Now when I am doing an upgrade I do atleast have a cursory look (actually more than cursory look) and see what updates I have. I had 100 updates from yesterday which were basically gcc and its pals, openjdk and its brethen and then little bit of mesa stuff. All of which btw is also known on the jaunty-changes mailing list (which I keep checking in as well) .
Now for last 2 days I didn't hear anything bad about gcc so that was good, none of other packages have anything to do either with booting up or with the networking so did it.
The only time I don't strictly update is when network-manager or any of the boot packages (say grub) new have been released.
Apart from that, unlike your experience I have experienced pretty good catches by forum-users and developers (where a certain update would disable updation or boot) . Been saved atleast 2-3 times although if I had to reinstall the system wouldn't have thought twice about it. That's the whole point of testing. To see what breaks and breaks where.
But the least the developers need to know where it breaks. Without our help as guinea pigs they would never know that for they haven't got
a. A wide variety of hardware b. Different ways in which a user may brick the system.
Automated testing may help but only so far.
That's my 2 paise :)