So how's iOS 4 Active Sync working for you? iOS 4 allows multiple ActiveSync accounts, meaning iPhone users can finally have their work Exchange setup alongside Google Sync, for example.
I've got both Exchange (2003) and Google Sync (Google Accounts) set up on both an iPhone 4 and an iPhone 3GS, and both mail and calendar are working fine (I don't sync Exchange contacts, never mind the mess that is Google contacts -- I use MobileMe for that).
Some users over on the Apple Support forums aren't having as much luck. Calendars in particular seem to be giving them problems where they weren't under iOS 3.x.
I did notice that, on my iPhone 3GS, the first time I added the second ActiveSync account the phone got hot and the battery started to drain so I deleted it, rebooted, and added it back and it hasn't happened again -- battery life has been surprisingly good.
What's your experience with ActiveSync under iOS 4?