A Whole Foods in NY has that. Everyone just gets into 3 lines and a note pops up telling you which cashier to go to. I think they have 3 lanes just to hold more people - the system would be identical with any N lanes.
I was at the one in Union Square (5 lanes express, 3-4 normal) and I've noticed that frequently the express lines will be totally full (10+) and on the other side of a small barrier the normal lines will have almost no one in them. Once I don't think I had any wait at all by not using the express checkout.
I sometimes wonder if people at the Whole Foods think they have to use the express if they have fewer than 10 items.
How about the Trader Joe's line? For those that don't know, there are two lines (express, non-express) that extend the entire perimeter of the store. I'm not joking, the line goes through aisles and blocks you from getting certain things.
The trick to this is to gather all the items not bordering the line, then get in line and shop while you advance in line.
