For the record, Ray’s argument swayed me and I upgraded (well, I love new stuff, so I was probably going to do it anyway 😉 ).
WP 2.5 really is lovely!
Only one thing threw me, and I think this happened to me before — when visiting upgrade.php, I just sat there, refreshing occasionally, expecting something to happen. I didn’t realise the big “Upgrade WordPress” at the bottom was actually a link you had to click! Could do with being styled a bit more “link” like. Or maybe it’s just me.