Thanks BigBad, yep, I have the .621 update. I assume there's no great loss in being stuck on 2.3.4 instead of newer versions? Looking at the 2.3.X release history, I don't see anything ground-breaking beyond 2.3.4, but it's hard to know what generic comments like "System enhancements" and "Camera software enhancements" include.
Like I said, the one thing that got me really curious was my co-worker's ability to select (and use) Tasks for syncing with Exchange ActiveSync. (On his 2.3.6 phone.) I see no mention of this in release notes after 2.3.4, but it would have been intersting to see for myself after upgrading. (And I really don't know what other explanation there is to him having Tasks on his phone.)