I know someone who had the EVO 4G (not sure if she ever patched it- she definitely never rooted it or anything fancy). She had 2 exchange accounts on it. The contacts she added on her phone never synced with exchange for some reason. When she removed her exchange account it still had all her exchange contacts on the phone.
I'm pretty new to android so I don't know if this is standard or what.
I know someone else who is thinking about getting the EVO 3D but has 3 email accounts all on different exchange servers. She's worried her contacts and calendars will get mixed up.