Originally Posted by ScareCrowe

Wow! 12.5% is rough! Where I am now it's just 7.25%.
15-20 is the % I would say to shoot for.

You mentioned huge parties and that made me remember something else.
If you have a large party and the restaurant tacks on a mandatory tip, Uncle Sam considers that amount to be part of the bill and servers are not required to claim it, the restaurant is. Uncle Sam considers tips to be obligatory in nature only, so by making tip mandatory it no longer qualifies.
Not helpful for us consumers, but if you are a server and wait on a big party with a forced tip, that tidbit of info could save you some $$!