This seems like the best place to post this; I just finished writing an application for OSX 10.5 that will launch a little server on any port you want and can tie to any detected usb-to-serial devices.  It's essentially a repeater; any messages from network clients are sent to all other connected clients and to a defined serial device and vice versa.  Designed to be a quick and easy thing to set up.

I know processing is more than capable of talking directly to an arduino or make controller, but sometimes when an idea is hot it's faster to just use something like this and make a tcp/ip connection than it would be to write and troubleshoot your serial code.  It's a gui app, but the php code driving it has been proven solid (one installation I did runs it for weeks at a time without restart and without any issues) so I'm hoping the migration from terminal to a gui hasn't hurt it at all.  That's why I need beta testers...  for stability tests, wish lists, and bug reports.

Here's the homepage:
http://www.rshieldslab.com/networking/socketserver-gets-a-gui/

Thanks to anyone that has time to play with this.