You wouldn't want to build Microsoft Word with it, but it is solid, mature, and robust enough for 98% of the GUI applications folks build. I've had tremendous success with it, and folks use applications I've written in Perl/Tk without ever realizing they are written in Perl. They get a nice interface, and I develop the application in half the time. Everybody wins.

I'd also like to suggest PerlApp since you sound like you work in the Windows world. It will allow you to compile your code and send Windows executables to your users so they don't have to have Perl installed to run your applications. I've used it to compile very robust Perl/Tk based applications, and it works like a charm.

Hope this helps :-)