It's not flapping in the breeze. Can't say how much difference it really makes. Normally I wear a loose fitting shirt made from some technical fabric or another. On a hot day I don't mind the extra airflow the flapping seems to bring. If it's really windy the flapping can be a little annoying but mostly I don't notice it.

I usually wear cycling shorts and I have picked up a couple of jerseys from ebay that I wear on group rides. I like some of the ones from Primal Wear but they're expensive to get through normal retail channels. The designs are interesting and they're not splattered with logos aside from the big "Primal" ones up the sides. Having the pockets in the back is handy as is the front zipper to control air flow.