He seems pretty successful to me. Unless you define success as being famous to yourself.
Guess, I got a problem with defining success of a person who works in a sphere that I don't know very well, unless there's an article in Wikipedia about him. That's my problem but I don't know how to resolve it.
I'd say Colin is substantially more "successful" than tarsnap has been as a business -- he's well regarded by basically everyone in the BSD community, crypto software community, etc. -- but that's because (IMO) tarsnap is a fairly niche product, executed well for that niche, but without much effort to make it a larger category product. Which is fine -- the effort to turn tarsnap into a more consumer-friendly or enterprise-IT-department friendly product might not be something he wants to do, and since he doesn't have external investors, no one is pushing him to do it.