Well, it's just my opinion and all, but I think what you get from a custom maker is this:
1. Pride of ownership.
2. Generally higher level of craftsmanship.
3. Literally, a product made custom to what you want.
4. Sometimes better materials and heat-treat, but that's not a given.
5. In some cases you do get a tougher product, but that's not a given either.
I don't think that a custom knife is going to work any better just because it is a custom knife. You may like using it better because it is exactly what you want, but 50 dollars doesn't necessarily perform and better than 500 dollars. Also, there are some very nice factory knives that use good materials and have great heat-treats.
I would venture to guess that most people that buy custom knives do so because they like knives and because in some cases, they do perform better based on their needs. For example, assuming that the maker is good, a 500 dollar chef knife is probably going to outperform a 10 dollar one from Farberware, at least in the eyes of a professional chef (and sushi chefs spend far more than that on their knives, man). In your eyes, you might notice a difference in balance or something, but if your only an occasional cook, are you really going to care? Probably not.
As far as sharpness goes, that is dependent entirely on materials and geometry. Assuming a factory and a custom guy use the same steel and at least similar heat-treating methods, I don't think one is going to outperform the other. I am not saying that steel is steel: hardcore knife knuts have very well defined and passionately held views on the pros and cons of different steels. I will say that I would guess that you get a wider variety of steels to choose from with custom makers, but if your a fan of some commonly used steel, my guess is performance is going to be at least similar.
Pride of ownership goes a long way too. A beautiful knife made to your taste is inherently more pleasurable to use than one that comes off the production line. Again, not saying that there isn't pride of ownership in owning a production knife, but if your the type of cat that is appreciative of quality cutlery, your going to eventually want a custom.
With all that being said, it's just my opinion, and I am not some expert. I am relatively new to knives as a hobby and passion, and there are collectors, makers, dealers and generally more knowledgable people on the subject than me. Jeez, I mean, I might even be WRONG about something!
As far as suggestions go, just use google and start looking around. There are lots of makers and a wide variety of prices. THR has a few makers that show off their stuff that you might be interested in, but there are so many makers doing so much cool stuff that it is a little baffling at times...