|laziness, impatience, and hubris|
- looks like the window manager of the O.S. (e.g. on Win32 it looks like the standard windows applications, so no look or functionality problems)
- relatively "hard" to program (it is strongly OO)
- on win32 its dll is 1250K + (it has to "wrap" the instructions to bind the API of the WM)
- multiplatform (soon also on Mac OS X)
- young (not wx library that is 10 yeras old) but it's growing up and it is developed by a IMHO great programmer, Mattia Barbon.
- not so well documented
- perl2exe is not working so well with wxPerl, perlapp ok
- it has its own look and feel
- well documented (a book) and supported (a newsgroup)
- mature software
- on win32 its dll is around 500K (plus other dll for widgets)
- both perl2exe and perlapp work well with Perl/Tk
If you need multiplatform you can look at Prima that is a GUI with its own look and feel, multiplatform, 2d design and animation oriented, with a lot of widgets.
If you're programming on Win32 you could look at Win32::GUI, that works only on Win32 but it is light because use Win32 GUI API "directly".