Really? And you know this because the number of Perl/Tk questions outnumber the number of web questions asked on Perlmonks? I think nowadays there's only one GUI that dominates the Perl world, and it's HTML/CSS/javascript.
That being said, the few times I've needed a pure desktop GUI, Tk was the best I found. It's old and primitive, but it works with minimal headaches on pretty much every platform you can think of.
"There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.