Purest don't like powder coat because it is thicker than regular paint. It will fill minor details like any cut outs in lug work, or similar.

Having said that, I've had several frames/forks powder coated and was always very happy with the results. Cost was around a hundred $... a bit more for extra top coats, (clear with sparkle, etc.) but wow did they turn out nice! The cost always included sandblasting the old finish off.

Find a shop that regularly does bike frames and you have nothing to worry about. They know what to block off and how to do it.