There is no money in it anymore. Everyone is doing it at prices too low for my blood.
This, I got into it a little time back, but now I have a few extra controllers and parts lying around that I don't have much hope of selling for much, but I often do it for my own personal use and for friends.
However, once the Xbox One comes out, there'll either be
1) almost no one making custom controllers for it
2) lots of people/companies will stop selling modded 360 controllers and start selling modded One controllers.
It'll be option 1 for the first few weeks, but making modded controllers has turned into a business for a lot of people, and I don't see them stopping when there will still be money to make from it.