I agree with Donald Denney on this. I went to an England PASS meeting on this two years ago, and the answer was "it depends". The biggest issue with virtualization tends to be capacity planning. If the physical box is configured correctly and the SQL server being virtualized does not have demands that will bring other VMs on the box down, then I believe it can be done safely. Not only that, but for things like SSRS and configuration databases that do not change much, it is probably a good solution for them.

On the other side of the coin though, I do not think that mission critical databases should go on them. There is a lot that I have read about the features of virtualization, but a lot of it has been stated without real-world data, so that leads me to believe they are selling proof-in-concept solutions, which I do not want to risk with my critical data. Also, some features such as virtualization snapshots are not supported by Microsoft under any vendor, including MS. I also do not think that it would be able to handle a replicated environment well either.

The choice is yours, but I tend to think of mission critical heavy OLTP instances as the last ones to be virtualized, if at all.