Having iChat problems? Fiddle with your router settings.

It has become apparent that Apple plug and play just doesn't apply when it comes to any sort of network applications.
Take for example the situation some users have apparently come across where uPnP* services need to be enabled or disabled on their routers to make iChat work.

The bottom line is, if you can help it, don't update your router's firmware until Apple finds a fix for this.

*(ironically uPnP stands for Universal Plug and Play)