After 'Leopardizing' my machines, I couldn't get my wife's MacBook to share the two USB printers that I have hooked up to my G4 iMac. I had noticed this new firewall in 10.5, and thought it would be a good idea to "Block some connections" -- not really knowing which ones it would block.
Well, it turns out that this setting was blocking the MacBook from trying to connect to the shared printers. Once I set the firewall back to "Allow all connections," the wife was happy again.

