We are currently on SQLServer 2008R2 and it is working nicely. Probably will not change for awhile due to:
Waiting until SP1 comes along, waiting until our vendor app is approved for upgrade, we are a small shop and see no big benefit from upgrading, I'm the only DBA and have enough work to do already, plus I have to justify the upgrade in the budget in some future year.
Other than that I'm all for upgrading. 🙂