Now that there is no NDA, what are some good suggested resources for learning about blocks under Snow Leopard?
This is a good introduction, and explains how to use a gcc patch to experiment with blocks under Leopard too:
Mike Ash has written two articles about blocks in his blog:
In a third article he wrote about Grand Central Dispatch, which is also using blocks:
Friday Q&A 2009-08-28: Intro to Grand Central Dispatch, Part I: Basics and Dispatch Queues
I would start with Apple's Blocks Programming Topics document or with Programming with Blocks on Apple Devices. As gs mentioned, also check out Mike Ash's articles (and also subscribe to his RSS feed, as I'm sure more blocks-related posts will come up):
If you're willing to pay the $300, the WWDC Mac session videos include several sessions on blocks and Grand Central Dispatch. The new APIs made possible by using blocks are also scattered throughout the remaining sessions that describe what's new in Snow Leopard.