I've been using my black and white set at the grocery store for several months and I get compliments on them almost every trip.  I also keep one in my purse and pull it out for small purchases at other stores.

Pros:  The small size makes them handy to carry around.  I put the set in my purse before heading to the store.  Each bag expands to hold about 3 plastic bags worth of groceries, so it makes carrying a whole cart load of groceries into the house much easier.  Of course, they are also very cute.

Cons:  It takes the grocery-bagger longer to fill these bags than bags with flat bottoms because they don't stand up on their own.  They aren't machine washable, but you can easily wipe them out if needed.  It takes about 30 seconds to roll each of them up (but the space saved makes up for this).