UPnP works in so far as giving an OPEN Nat result, however, port forwarding will be needed to obtain full connectivity on a very select few games.
The real acid test, as I've found over a few years (and a few different routers), is the game COD3. If you can connect to any game without seeing the dreaded "Could not connect to all players", then you have a perfect connection.
If you see this error though, you DO need to forward ports.
