"Street" photography has to tell a story - the image should, imho, tell us something about what's going on..
Classic street photography, back in the "golden age" of the 50's, was awesome.
Photos of people walking away from you, unless the image tells a story, are indeed boring - I've shot tons of those but the only one I ever liked was an image that portrayed young lovers.. that's it.
So many people think they can walk out there with an M or SLR and shoot the most mundane crap and suddenly it's "art"...
I miss the days when cameras weren't as prevalent as they are today... everything is a camera, everyone is afraid of a camera, and everyone has a camera... makes for exciting images of people trying to hide, cover the lens, or charge you with violating their "privacy" in the public space..
Dave