For those who use UPnP and are comfortable about the security implications.
I've found a tool which allows me to open ports at will. I've found this useful since it means I no longer have to leave ports forwarded all the time for games etc. I can just forward them while I need them.
If anyone is interested in this tool, or knows of a good tool for the same task, then post here and let me know :-)
Ps I know some applications e.g. MSN Messenger already do this, but many applications don't. In addition using this tool, I control what ports have been opened.