I had my Santana tandem powdercoated earlier this year in a metallic deep red. It was a two-part process - silver metallic base coat, then translucent red topcoat. The two-part coating is pretty thick, but the frame was TIG welded, so no worries about losing lug details.
The shop that did the work had experience with bikes, and they do a lot of of motorcycle work so they're familiar with dealing with tubing, but I still felt compelled to point out how thin the tubing was compared with a motorcycle frame. The end result was pretty nice, though there are a few small areas where some pitting is evident under the coating. I needed to chase most of the braze-on threads even though the shop did their best to mask/plug them. There was also quite a bit of blasting grit inside the frame, I blew it out and applied frame saver.