[mr_dbr]

It would be nice if this was back-ported to Leopard (so you could use GCD without the application being Snow Leopard only), I wonder how difficult this would be..

[jsz0]

More than $29 worth of difficult. That's for sure.

[antonovka]

http://code.google.com/p/plblocks/ is probably the place to start.

[pohl]

Without special kernel support, you could probably, at the very least, get a thread pool that was local to the process. That might be worth it.

[GeneralMaximus]

IIRC, you already have libraries for thread pools on Leopard. Core Foundation would be where I'd start looking.