I get a nice square angle, never had any problems. I've only ever tried an angle trowel once and it dug the walls out either side - to be fair the walls ran out something stupid - but it left a mess. I might give it another go from reading this thread though (the adjustable jobbie posted on another thread looks intereting).
Preferably I skim opposites to get hard angles but have no problems doing wet.
As an asside when I first started and I was being tought, one technique was to finish the angle then run the corner of the trowel lightly down the angle when dry. Whether it makes it look sharper when painted I don't know, I thought it looked crap.