I received my DX one week before the OTA and it ran beautifully on the original 2.1 OS. I did the upgrade yesterday afternoon and...it STILL runs beautifully, with one exception - its now faster!
I love this phone, especially coming from Palm OS, which I seemed to have nothing but problems with the past year (this prompted my switch, even though I've been a Palm user since my first smartphone in 2003). Is the DX perfect? No - there are even some things the Palm did that my DX can't do as easily (sync to PC, BT tether to my Powerbook G4, sort phone contacts by last name, for instance). But the added functionality, screen size, speed and so forth are such an improvement over my previous phone - its a Buick to Ferrari change for me.
I haven't had any major problems with the phone like others here have posted