Yesterday, I raised our DFL to 2008 R2. Pretty simple once all the domain controllers in your domain are up to 2008 R2. Pretty much, right click, "Raise functional level..." choose Server 2008 R2, and OK. Once raised, replication across the domain will take care of the other DC's.
I did make sure to research any issues that might come up after raising the level. The only forum I really found was someone having issues with a third party app performing an LDAP search. I will keep an eye out on our applications that query LDAP, such as VoIP.
Now we wait until all the other domain administrators in our forest update their domains to 2008 R2, so we can update our Forest Functional Level.
