As someone with a fair amount of Tcl and Tk experience, I think the web is the way to go. It's simply faster and cheaper to develop and deploy with. Fix a bug? All you have to do is upload a new version to the server.
Here's patio11 on desktop vs web: http://www.kalzumeus.com/2009/09/05/desktop-aps-versus-web-a...
That said, Tcl and Tk are a fun, fast way to hack up little applications if you need something local.