Just thought I'd share my experiences on this...
After upgrading from 10.8 to various DP versions of 10.9, the Messages app was completely non-functional. Despite having network interfaces set up properly, a recovery partition present, NVram and Chameleon set up correctly and a working serial, the app still was totally broken even though it was previously working under 10.8. DP5 for instance presented no password field at logon and a strange and unpredictable UI. DP6 was even worse, just a blank grey window. I've heard of at least a few other people experiencing these problems too in the main 10.9 DP thread.
After creating a new user account and opening messages to find it working perfectly, I concluded that it must be a problem with my user account data. So I replaced all the directories or files I could find relating to Messages (also sometimes called iChat) in the Users\Main User Account\Library (hidden) directory and all of it's subdirectories with their counterparts from the same location in the new user's folder.
Not sure exactly what files did the trick, but when I returned to the main user account, it worked perfectly.
Users\Main User Account\Library\Containers\com.apple.ichat
Users\Main User Account\Library\IdentityServices
Users\Main User Account\Library\Messages
Under Users\Main User Account\Library\Preferences I spotlight searched for any file with "ichat" or "message" in the file name and replaced them. Altogether there were about 20.