the $640 you're talking about - that's for four tickets, right? Face value?
I would be very careful of any tickets on Craig's List. Don't go for any transaction that involves going through an "ebay agent". You might want to check out the posts on ticket scams and scalpers on the Telluride ticket exchange board.
The e-tickets are convenient in some ways, but they do make it easy for slimeballs to sell the same ticket over and over. Get as much info as possible on the seller.
Don't forget to check the Returned Ticket Resale page on the Planet Bluegrass site on Tuesdays at noon Mountain time.
http://shop.bluegrass.com/index.php?main_page=index&cPath=93