Sorry, got sidetracked!

Thanks Perry, I somehow missed that entire section on removing patches!

Thanks for your reply too Steve!  I had not considered what might happen if an SP introduced a new feature.  Aaron Bertrand has a write up about moving databases between SP's and mentions the SP you bring up.  According to his test, you can downgrade a 2008 database from SP2 to SP1 provided you do not enable the new partition limit on any databases.  Perhaps this will hold true for failover downgrades as well?

Still, his blog mentions a number of caveats and seems to suggest caution.  Sounds like the message here is to test it first (of course!), but I unfortunately do not have an environment to do so on.  Thanks for your input everyone!