First, lets get this straight. Powdercoat is not paint, it's plastic. Powdercoat doesn't contain "hardeners", it's not paint. Powdercoat is essentially powdered plastic and is applied as previously described (negatively charged part and positively charged plastic powder) and then baked. Powdercoat is more durable than the best paint job but does have some drawbacks. It is relatively thick and can pose problems when one part has to fit over another (downtube shifters over powdercoated shifter bosses, for example). It can't be applied to all types of materials because not all materials can take the baking process (around 400 degrees, give or take). Regular decals don't work well. They make decals you can put on that will stand up to the baking under a clear powdercoat. You can also put on vinyl decals over the top after coating and baking. You can make powdercoat do just about anything paint can do. As Hecubus said, some can do an amazing job like spectrum powderworks. However, the skill, techniques and equipment needed to do this kind of job is not as available as paint.
That said, even a run of the mill powder shop can do a great job, especially in a single color. Often it is VERY cheap. I've had three frames done by a local shop that does mainly farm machinery, industrial parts and race car frames/parts. Each one cost me $50 and that included all the prep work (taping, bead blasting, coating, baking). They turned out great. Look great, very durable.
