Someone else has probably done this as well, but I’ve updated Twitter Updater to take care of a few outstanding issues.  It now uses phpCurl and checks the zz.gd/tinyurl.com output for validity before putting it into your status update.

Twitter Updater

I’ve tested it with my 2.6.3 installation.  It should work on any WordPress 2.5 or better with phpCurl enabled.