Update: Matt Cutts responds here.
The spam issue is a real one for all social applications, which includes search, of course. But I hate the baby with the bathwater approaches. I think we need to get to the next level of validation with social media – we need to start getting more granular. As humans, we’re pretty good at weeding out who is a normal person worthy of whuffie, and who is a skeezy slimeball out to take advantage. Can’t we do the same on Twitter?!