I have a friend I met in Portland, Maine named Slaid Cleaves who is reasonably sucessful now who would be proud to tell you that he learned his trade on the corner of Exchange and Fore Streets in Portland's Old Port District. He did some great yodeling, Hank Williams, Woody Guthrie, popular tunes as well as his own material. The local shop keepers are notorious for trying to rid the streets of musicians or anyone who they thought was blocking the sidewalks, although many people come to Exchange Street for the entertainment.
I know the Boulder Mall has been famous for its buskers. That is a touching story about the magician, though.
Brían