I am a physicist working on the Laser Interferometer Gravitational-Wave Observatory (LIGO) project. One of my colleagues is Phil Ehrens, who is well known to many Tclers. I started using Tcl/Tk in late 1999 and have done several very useful things with it (if I may say so myself). The first project I undertook, a GUI for accessing LIGO data, is written in pure Tcl/Tk and has grown over the years to more than 22000 lines -- all in a single file! Some people may find the idea of a 22000-line Tcl script appalling, but it avoids any kind of installation issues: just put it wherever you want, on any computer with Tcl/Tk installed, and execute it. (This pre-dated the introduction of starkits by a few years.)
You can see me (and the two computers on my desk) here: http://www.ligo.caltech.edu/~pshawhan