Acoustic Roots/Medley Music in Bryn Mawr has a resident repair guy, Dave Dougherty, who does great work. He's done work for me twice before and I've been completely satisfied with his work. It's a little far from Princeton, though.

There's another guy, Jack Romano, in Conshohocken PA (again, not near Princeton) who comes very highly recommended by a good number of people I know, but I haven't had the chance to try him yet.

-Greg