PGP’s web of trust hasn’t been a mainstream success because (and I say this as a dedicated GPG user) the UX is awful. I don’t think it has anything to do with the web of trust though; in fact GPG doesn’t really expose the web of trust ideas much to the user.
I can easily imagine a web of trust system with UX more similar to Facebook’s (and in fact this is basically what SSB’s clients are).
I can easily imagine a web of trust system with UX more similar to Facebook’s (and in fact this is basically what SSB’s clients are).