I like it, and yes, I'm sure you can combine it with social networks to get something compelling (e.g., you can make it cheaper to send email to people who have designated you as a friend, etc.). It's strange to see the overwhelmingly negative reaction on TechCrunch though.

Well, because it won't eliminate the junk messages vying for my attention, it will just earn me fake email currency for reading them. This does not help the overall goal of email overload.

If I trust the person sending the message, he/she can just use the "Priority" feature. If I don't trust him/her, then I don't see why messages with more virtual currency units are necessarily more important than those with less.