I've just started to use them. The guy who taught me to cut and sharpen with a laser was anti-microbevel, so I never really tried before. Plus, I assumed that stropping and general imprecision would automatically give a bit of a microbevel. Recently Jon at JKI encouraged me to try them for real (I was asking if he thought I'd get better edge retention out of a Suisin or one of his Gesshins than I got out of my Tadatsuna; he said noand that I needed to wake up and use a microbevel). He suggested a hair's width, at 30+ degrees, just on the face side.
I've tried it with maybe a 20° microbevel. So far it's made a big difference. I can't feel any decrease in performance but my edge holds up to much more abuse, and touches up in just a few seconds when it eventually looses its glory. Next time I sharpen I'l try it at the more obtuse angle.