It's not hard to learn at all and the GUI API is about a billion times cleaner than Java's swing. Pick up O'Reilly's "Mastering Perl Tk" (the emu book) if you can spare the change, as it really is an awesome reference on the subject.
I am currently considering writing a Perl/Tk SimCity clone (ambitious? YES!) just because it CAN be done. The Tk part is very easy -- it's the algorithms part that is challenging. Tk is poorly suited to games that do a bunch of really fancy rendering, but it can move things around on the screen (with a fixed number of objects/sprites) pretty darn well. I keep thinking YetAnotherScorchedEarth would be a good idea. Arrows and other primatives animate very smoothly.
Anyhow, I'll check this program out when I get home -- not a good idea to play with camels at work :)