I also wanted a collar for my Jasmine who is microchipped, in order that people know she belongs to someone if they see them outside, but I gave up, it was too dangerous in her case (see my old thread http://petoftheday.com/talk/showthread.php?t=99998). She just can't stand it, while Peppito wears a collar without any problem.
But I guess only a minority of cats react like here...