alt Hacker Newssame - I check the changelog for every major (== minor if v0) and some minor version changes in most of my projects, including at work. I've caught quite a lot of would-have-broken-something changes, and opportunities for fixes/optimizations/etc by doing so. and sometimes they mention fixing a bug we didn't know we had, so we learned about it early before it corrupted too much data.
It's nice to have that luxury, we just don't have the manpower to devote to that. Major versions sure, otherwise it's just update and run test-suite and some smoke tests.