In the interests of making some of my reservations more believeable (and I'm sure there's ego involved somewhere too;), I've been using Tcl on and off for five years. I've also written about 5000 lines of Tcl code for Web sites using the ACS in the last year -- I've run into several limitations, and part of the plan with PyWX/Python is to reduce or eliminate these, while making the transition so easy you don't notice... which isn't that hard. We'd also like to retain full Tcl functionality (which Brent was initially unhappy with, but I convinced him rewriting the ACS was a Bad Idea ;).
I'd also like to note that PyWX has gotten a nibble of interest from several ArsDigita people. The main objection I've heard is that they're too busy writing sites to worry about the language, which I suspect is going to be the dominant objection.
PS the main limitation, for me, is reusable & extensible code. I find myself writing the same damn functions over and over again, with minor variations... ugh. It's like I'm writing in C again...