I'm using fully updated Tiger and not seeing anything like the problem Manny is describing. Of course, I'm still stuck at low-ID, so I might not be exercising the OS's network parts in the same way. However, I doubt it's the system update.
It might be that your ISP has started to punish people who run p2p file sharing programs. It might also be that your router has gotten itself into a weird state. You might try rebooting it and/or turning it off, waiting a few seconds, and then turning it back on. Also, you might try lowering your preference settings for Max. Connections, Max. New Connections / 5 secs, and possibly your Upload and Download Bandwidth limits.