I usually tip about 18-20%. A lot of the servers around here are college students just like me who are trying to make money to pay their tuition. Serving is not in their future career plans. I've never worked as a server but, in my opinion, I see it as one of the most difficult and thankless jobs. Working in retail, I've seen customers who will get angry over things that aren't your fault or take their stress from a bad day of work out on you. I can only imagine it being 10 times worse in the restaurant business since you're dealing with people's food.
If the server was absolutely horrible, I will tip 12-15%.
Servers live off tips. Their wage is only $2 an hour plus tips. Yuck!
As for the to-go people...I will usually tip 15% since all they did was just wrapped up my food. Usually being the key word. I had some horrible service at Chili's To-Go last month. This girl was so mean and rude that I actually told her to her face, "I refuse to tip you" and I drove off (as fast as I could
).