SLEEP_TASK Wait Type in SQL Server - What does it indicate? I haven't seen the SLEEP_TASK wait type before, and today I seem to be getting a ton of them.

I'm not the official DBA, just a SQL Server developer who knows some DBA stuff.  We upgraded our servers last weekend to 10.52.2500.0 - R2SP1 I think.

All the info I could find online indicates that SLEEP_TASK means the server is waiting on some sort of internal process to  complete.  I don't have any blocking or any background processes like checkpoints or ghost cleanup running, so I'm a bit stumped.

Has anyone seen this wait type before, and if so can you give me an idea of what is causing it?
SLEEP_TASK is a general wait, used for all sorts of things where a more specific wait type doesn't exist, but it does crop up with hashing operations (join/aggregate) that spill to tempdb, and occasionally at an exchange (Parallelism operator) where a consumer is waiting on something that isn't a normal CXPACKET or EXECSYNC wait. I would check for Hash spills first.