A plus from me too. Besides the fact that Tk is seen by many as ugly, I see very little shortcomings.
Tk is actively maintained and builds on most OS's out of the box, including HP-UX, AIX, and Windows with Strawberry perl.
The documentation is complete, and almost all fuctionality is available. It is very hard to make thing like rotated text on a Canvas, but if that is what you need, you might find some more luck in using Tk::RotCanvas or Tk::Zinc.
After installing Tk, there is a demonstration script called widget, from which you can cut-and-paste code to get started.
I found it very very hard to create a working anvironment on AIX and/or HP-UX to get Wx running, and I also dislike the immensely complicated (but complete) documentation for Wx. It just takes too much time and coding to get started, and if GUI programming is not a daily job, it is hard to remember all the ins and outs for Wx.
Playing directly with X11 modules is only for the masochists.
Enjoy, Have FUN! H.Merijn