In order to get threads in tcl, you must build tcl with thread support (which we do) PLUS after the install of tcl, you must build and install the actual threads extension available as a seperate download from http://sourceforge.net/projects/tcl/ (which we don't do) I propose that an ebuild be added for the tcl threads package and that the "threads" USE flag cause it to be a runtime dependancy of tcl.
fixed(dev-lang/tcl-8.4.11) in cvs. thanks.