There seems to be another alternative, called WxWindows which aims to be a platform independent GUI for at least Windows, X and Mac. They have Perl bindings available at WxPerl at Sourceforge.

I haven't tried any of these yet though, but it looks like a very stable, well documented API.

Jouke Visser, Perl 'Adept'
Using Perl to help the disabled: pVoice and pStory