I never heard of a phase change vest until this thread. They look interesting. Unfortunately, they only work for a few hours and then have to be put back in the freezer. Even still, they would be great for a Sunday ride. I don't think they would be of much value commuting because they probably wouldn't be necessary in the morning and by quitting time, they have already thawed out. Still, I think I'd love to have one.
http://www.polarsoftice.com/bodycoolingphase.html
As for me, I wear mesh here in South Florida. Its not perfect, but its the best way to keep from having a heat stroke on the bike during the 11 months of summer. I've seen perforated leather, but I just can't imagine it letting as much air through.