I recommend testing the port you have opened for BT traffic at
ShieldsUP. You can enter the port number there and it will tell whether it is in fact open.

If ShieldsUP tells you the port is open, then the problem lies elsewhere...

Update the firmware on the Router if you have not already done so.

When using Azureus, remember to Choose a Port or two ports (dont use the default), Open the port at the linux firewall (remember to open both udp and tcp), Open the same port(s) at the Router, then test using a linux distro. If you get a green smiley face you are in business.

Other problems could include.

Your ISP blocks bittorrent traffic.
- Go to Tools > Options > Connection > Transport Encryption
- Tick the "Require Encrypted Transport" button
- Untick both the "Allow non-encrypted connections buttons (incoming/outgoing)"
- Tick the "Use Cryptoport" button

Restart Azureus and try again

Or.

The dodgy system-config-securitylevel program that doesnt remember custom ports unless you use the following workaround.
- Add a new custom port.
- Tick a trusted service (any will do).
- Hit Apply.
- Close the program.
- Reopen the program.
- Untick the trusted service.
- Hit Apply.
- Close the program, but your custom ports will remain.

My ISP doesn't block BitTorrent because it works on other systems and when I open the Security Level Configuration the port is identified as open.
I tried ShieldsUp and it said Stealth. I'm switching distros.

Just for what it's worth, I have recently tried the latest Azureus (Vuze) and it doesn't require you to specify a port as previous versions did. It just works.

Does it do that by means of Universal Plug and Play (UPnP)? If so, you will need a UPnP-compatible router; not all are.

That must be it, I guess, as I see that the FAQ does still mention port forwarding: http://faq.vuze.com/?View=entry&EntryID=96
Only for the first time I don't seem to need it anymore.