I wrote a app that is similar to the "serial proxy" on the arduino download page. My version does not require static IPs or holes in the firewall as it proxies bidirectional end to end serial over XMPP/Jabber/Gtalk.
It is written in Java with start up scripts for Mac, Linux, and Windows
I wrote this with Arduino in mind but it is not Arduino specific. I hope this will allow some Arduinoers to make some cool remote interactive stuff.
Gustav von Roth