• The biggest problem I've heard about is the lack of additional tuning done with the ORM tools. Implicit conversions with varchar -> nvarchar (and vice versa) can be an issue, and blow your indexes out of the water.

    There are also issues with no tuning SQL, or perhaps not re-examining the way the objects are stored and cleaning them up. The ORM might do things like drop LOB data in your table, but you might want a vertical partition to allow for online operations on a busy table. This is in addition to cleaning up the ORM calls and substituting in stored procs in places