I'm relatively new to the b-bag world, but I think I just bought my second in a week. YIKES!
What I love about them: great design with a look that changes depending on the color -- and the colors are fantastic. Unlike any other bags out there. I see the First as an evening bag, and I bought it in Marron, which I think is a very sophisticated color. Twiggy is dressy fun (and I just BINed on auction for one in Rouille, but haven't heard from the seller so I'm nervous), so I've wanted that in Rouille and Blueberry. City is classy casual, so for me I want that in Ink...etc., etc....
What other bags have that chameleon ability? And I'm sure you all see the bags differently and have different philosophies about how they fit into your lives. That is the sign of a GREAT BAG!