Ah, this is fascinating. I'm writing this in November, and actually started noticing the problem not with Google Street View, but with text in Flash movies. The Flash movie would work perfectly, except some text would simply not render. Google Street View not working for me was a secondary symptom. (FWIW, I experienced the exact problem seen by others here: GSV didn't work for the Admin account, did for a Guest, no amount of prefs/plist trashing or plugin reinstalling would fix it.)
I'm not at the computer experiencing the problem right now, but this fonts thing is hugely encouraging. I'm looking forward to trying this as a fix!