I'm playing around with Twisted and documentation found on their homepage doesn't answer all my questions.
The topic I am most interested at the moment is Twisted Application Framework. Also some open source servers using twisted framework would provide nice material for studying how it's all tied up together in a bigger project.
So far I've checked out iCal and read documentation on twisted website (3x) and few good articles I found in google.
The published book is pretty useless, in my opinion.
I recommend starting with the "deferred" docs online, and making absolutely sure you understand what asynchronous means and what deferreds are for. The best online docs that I've found are on the official site, though they could surely use some polishing:
http://twistedmatrix.com/trac/wiki/Documentation
The developers recommend reading the source as well, though if you have specific questions, I've found that the devs hang out and respond on both the IRC channel (#twisted on the freenode network) and the online mailing lists (There's a general and a twisted-web specific list)
As for blogs, there's at least the two below (both blogs are by twisted developers). I bet if you asked this same question on the twisted-python mailing list, you'd get a much better and more comprehensive answer than I could possibly give. :-)