I'm a little taken aback by how seemingly easy it was to use the built-in automatic upgrade feature in MU 2.7.1 to upgrade directly to 2.8.2 (skipped 2.8.1 entirely).
On my test server, I initially tried the upgrade manually by copying over all the old core files, etc., and pointing to the upgrade script in my browser ... the result was like any other upgrade I've ever experienced: sitting and watching as MU upgrades all my blogs five at a time.
So I noticed the automatic upgrade is now native; I then reverted back to my 2.7.1 installation and its database to test it out and it behaved like upgrading a single installation of WordPress--just a few confirmation lines in the dashboard, nothing more. No cycling through blogs 5 at a time. I then read this page: http://codex.wordpress.org/Upgrading_WPMU, specifically the paragraphs about "What does the upgrade button do?"
This page isn't updated to include moving from 2.7 to 2.8, so I have to ask: So, when users log back into the dashboard, that's when they get updated? I checked out some of my user accounts, and sure enough--they're on 2.8.2.
This is great, but seems too easy compared with upgrading MU in the past. I suppose I need some reassurance to confirm this is what's to be expected from upgrades in the future.
And if so, amen!