Our restaurant also uses Groupon's POS and payments system. "Moderately successful" is how I would put it, although version 2 has improved things considerably. There is pressure to find a better POS, but I have yet to see one that I like. Most other point-of-sale systems that I've seen either fall short on everyday things like splitting checks, or they're technologically terrifying. The last demo I saw was of a cloud-based system with online reservations, and it looked alright up until I realized that the terminal was running Windows XP. This was last fall.