I've used PAR to compile a Tk application (the woodlice.pl script I bundled with Tk::Taxis), and the executable works absolutely fine, despite the module using Tk, a hand-rolled event loop, Time::HiRes and a subclassed Canvas widget, all of which I thought might cause trouble. The only two issues I had were that the Tk::Taxis module did a use 5.008;, and the PAR I had installed whinged about this - not sure if this was due to PAR itself, or the fact I was using a ppm-installed version rather than compiling it myself - but commenting out the offending use statement fixed this. The other issue was that the module used some JPEGs in the canvas, and these (not being found by Module::ScanDeps) had to be bundled separately from the PAR executable and the path to them hard-coded into the module. All in all, it only took about ten minutes to get it to work. I've not tried it with threaded designs, but considering how little hassle I had with this, I'd be surprised if they caused any more trouble under PAR than they are prone to under normal perl.