I would totally give a busker some BTC if they had a visible Bitcoin QR code up. I rarely have small bills or change on me but I always have my mobile Bitcoin wallet app.
I'd sooner do
one of those QR-code things that puts a $2 or $3 tip to me via paypal
??
nah, have 2 QR codes, one with a paypal logo under it and one with a bitcoin logo, obviously the Qr codes above them will contain the particular email/bitcoin address it pertains to. after all what is there to lose by having both