The only thing I would say to watch out for is to make sure that when they are doing the work that they carefully cover up all the holes and openings in the frame. Also, they should know to cover up any threaded eyelets (e.g., fender eyelets) so they don't get coated. My place did a great job but they forgot to cover up two fender eyelets, and I ended up having to clean them out.

Also make sure you are using a coating that it is intended for outdoor use.

This is the place I used - they have good info on their site, and links to several of the major providers who provide the powder (Tiger, Cardinal, etc.)

http://www.seattlepowdercoat.com/colors__textures

The biggest advantage to powder coating IMHO is durability and cost; much cheaper than a high quality paint job.

Disadvantages:
- an inexperienced powder coater can put on too thick of a coating, will cover up details in a lugged frame if that's what you're working with
- I've read that they are hard to strip and re-coat, if you ever want to do that