Well I have only had it for 8 and a 1/2 hours now, And i came from 4.5.0.51. But to be honest, I never had any problems with 4.5.0.51, and don't see any new ones in 4.5.0.66. So its nice so far. I do however always get my LED light stuck on since .51. Maybe its just cause my program BlackBerry Alerts doesn't work well  on 4.5 beta. Dunno. And I still see the little black box before the date in SMS messages. But looks fine, so it doesn't bother me.

Any other users, please post your findings here too.