If you're having trouble using Google Talk, don't waste time messing around with your network and/or router settings. Chances are the problem has nothing to do with you, Joe User, with the culprit being something on Google's end. The sultan of search began investigating "reports of an issue with Google Talk" early this morning, and within 10 minutes, determined that whatever it is that's causing the problem is affecting the majority of Google Talk users.
Google began investigating the issue at 6:40AM. At 6:50AM, Google said it was "seeing error messages and/or other unexpected behavior" and promised to provide a ETA by 7:50AM on when the service would be restored. When 7:50AM rolled around, Google pushed its ETA for more information to hour later, and then again when 8:50AM rolled around.
Whatever the problem is, Google seems to be having a bear of time wrapping its engineering heads around it. Information is pretty sparse at the moment, but according to reports around the Web, the massive outage affects users in all corners of the world.