Custom is pretty cool and there are tons of excellent framebuilders out there. I just can't justify the cost for the average joe who isn't racing or for someone that doesn't need a custom.
People get custom because they can't find exactly what they are looking for off the rack. It mainly comes down to about fit and experience, and then sometimes the artsy thing. If you have the experience and know you want a modified geometry that you can't obtain off the rack, then custom is a great alternative. If you want some really cool stainless lugs ornately cut into a pattern (like Vanilla frames), then good luck finding that anywhere. You're next best bet is custom.
For the average joe, it's a no go.
For the $$ discerning buyer, custom may be the route.