launching UNIX apps from MAC via SSH

Hi,
I am new to OS X (coming from Windows, and NOT regretting at all;D) and began to play around with Terminal and SSH potentials, I got at this point where I need to make a question like this:
at home I have an iMac powered wity Lion OS and a PC that has been converted to Linux OS (Ubuntu distro 11.04).
I discovered the potential of SSH tunneling and X forwarding, and succeeded to run X applications resident on my Linux PC on the screen of the iMac (i.e. Gimp, xcalc, xeyes etc.). Pretty nice.
I also succeeded to access my remote filesystem in both directions (i.e. accessing Linux filesystem from Mac Terminal via ssh and accessing Mac files via Linux ssh session).
I could even launch Mac apps from Linux via ssh (i.e. from Linux terminal connected to my iMac, launching the 'open *.app' command), with those apps showing on my iMac screen (my Linux being a sort of 'remote controller' of my Mac).
One thing I didn't succeed was the opposite from the last point: I cannot launch Linux applications ON Linux screen FROM my iMac via ssh.

Both my systems are configured in order to allow X11Forwarding (I edited the sshd_config on the two machines removing the #sign and writing 'X11Forwarding yes'). I've been reading around but couldn't find a solution to my problem.
Does anyone know what I am missing here in order to proceed with this last bullet? Everything else is working fine.
Thanks for your precious help

Don't use X11Forwarding. If you forward X, the apps will open on your Mac - that's what X forwarding is for. Disable X11Forwarding and try again.

thanks vansmith.
I also tried by simple typing of 'ssh user@address' (without the -X option) on my iMac and then launching commands such as 'gimp', but on the Linux screen I won't see anything, and on my Mac Terminal connected to Linux I get 'can't open display' sort of messages...
any clue of what I'm still missing?