SP1 has been out for a month now - and here's my experiences so far.
Please comment, if you have any :-)
Of course SP1 is unavoidable because of all the new features and bugfixes.
But had a litte trouble after the upgrades.
Every Nokia mobile running Mail For Exchange (MFE/Mail4Exchange) had problems.
Some could be solved running a Full Resync, several times, but most had to delete the MFE profile and recreate it.
This was with various Nokia models, and most of them was running newest version of MFE.
This is most likely a Nokia problem, but will still prevent me from installing SP1 for customers with a lot of Nokia users.
The only other "problem" i had, was that Backup Exec required to be updated to "Backup Exec 2010 R2", and this of cource requires you to buy a new license, unless you have subscription on the product
Beside from that I haven't experienced anything that's not in the Exchange teams own blog: