DACP is similar to the well-known DAAP, using Bonjour MDNS to find libraries, then using HTTP requests with binary responses to transfer data. After a few days in front of packet dumps, I have most of DACP decoded.
With the protocol now reverse engineered, I wrote an Android client in about a week. Now you can remote control your iTunes from your new Android phone when it arrives later this year. This works out of the box without installing any extra software on your PC or Mac. Here's a quick video in action on the emulator:
Android iTunes Remote Control from Jeffrey Sharkey on Vimeo.
If you're interested in jumping right in, here's an APK ready to install. Also, the full source has been released under a GPLv3 license, and you can grab it from Subversion on Google Code: