coexistence exchange 2010 SP1 with exchange 2010 SP2

Hi,

We have several exchange 2010 servers with SP1 (and latest rollup-updates) located in several countries.   Each Exchange server have their own administrator.  Countries represented in separate Organization Units in Active Directory. It is Windows 2008 R2 DCs, single AD domain.

I have an intention to upgrade my Exchange 2010 SP1 to SP2, while the other remain in SP1 (since they all not maintained by me).   

Additional note:  i had just migrated exchange 2003 to exchange 2010 (new box).   All mailboxes had been successfully moved to exchange 2010.

The questions:
a. Any issue may rise to other Exchange 2010 SP1 servers?
b. Any reference from Microsoft?

thanks in advance.
regards.