Yowza. There are very few things that make me happy when I'm programming, and Twisted is definitely in there. If you can think of a protocol that sits ontop of TCP/IP - it's probably or it's being worked on. Some of the finer features I can imagine using are the SSH client/server to remotely instrument an application to figure out what the heck is going on when an application is running live. Sweet.
My only small - really small - gripe is that the documentation is slightly out of date. I had to play with the twisted.enterprise code a little to get non-blocking database access working, but hey - it took 15 minutes. It's just nitpicking at that point.