I've used TCL in production for 15 years. The only thing to really worry about is a consistent policy on language usage. Keeping to the base features of the language and extensions in tcllib/tclx is a pretty solid recipe.

That said here are things I advise.

* No upvar/uplevel. Use a namespace. * Use apply wisely. * No ad-hoc (say swig inline wrappers) extensions without deep review. * If you are writing a front end in tk - think twice. * If you are doing OOP with TCL choose wisely.