I second dfcleanowned. It is fast and simple. These other methods get really painful once your dwarf count gets north of 50. If you're using Dwarf Therapist, which reads and writes from DF memory, then you should have no problem with dfcleanowned (besides having to execute it from a command shell).
Admittedly one key difference between Dwarf Therapist and DFCleanOwned is that while they both write directly to DF memory, DT only does so in ways you could have done yourself (although very tediously in some cases) through the DF interface.
DFCleanOwned allows you to *confiscate* (remove ownership of) items arbitrarily, which you cannot do through the regular interface. Normally I'd consider that "cheating", but the way I look at it I'm just working around a bug. I can't imagine the current situation with dwarves wearing rotting clothes (and getting unhappy thoughts about them) until they disintegrate all while claiming shiny new clothes that they never wear is how Toady intends for all this to work, so I don't mind working around it with a hack for now.
I mean, has anyone noticed how the "Refuse" stockpile has options to accept worn out clothes, yet no worn out clothes ever get put there? It will be a very happy day when the bug is fixed and dwarves toss their own worn out clothes in the refuse stockpile without having to resort to hacks.
--nomad_delta