Flightaware.com used Tcl as one of its foundational technologies. Karl Lehenbauer gave a presentation in which he covered some of those systems: https://www.youtube.com/watch?v=3YwFHPFL20c
I use Tcl daily for work and personally love it! Its syntax is weird but when it clicks things just make sense in a zen way. Much like getting into the groove in lisp or something, it _feels_ correct in that minute.
The main problem is just tooling. There are some insanely cool language features like Expect (still the best implementation) or starpacks/starkits, yet there is no basic package manager. You are stuck installing via yum/apt or building from source if you are lucky to find what you need. Most of the time you can just assume there isn't something you can rely on, and you'll have to patch source tcllib (the batteries included library).
