My take on this is that if you and your users are happy with your current builds then there is no reason to rush down the upgrade path. If you have compelling reasons to migrate due to Bugs or "feature" changes then, of course, look to move ahead. It's not like your running Unity 3.x and Callmanager 3.x ;-)
Have a look at the attached doc I put together that highlights CUCM feature changes up to and including CUCM 7.0 (I'll add 7.1 one of these days)
I'm not able to access my old voice mail messages all of a sudden. The recording says something like 'the message is currently not available'. This has never happened before in all the years I have been using this system. I have t...