I tip 10% at counters such as Starbucks, Baskin Robbins, pizza pick ups, etc, and at smorgasbord restaurants where the server only brings you drinks and the bill (UNLESS s/he does an outstanding job).
At normal restaurants, I tip 15% if the waitress/waiter is nothing more than adequate. If the server is good, then I tip more according to the service that I got, sometimes up to 30%, but usually around 20%. If we take up the table for a looong time, because I am visiting or conducting a meeting, then I leave a tip that makes up for the customers that the server missed because of me.
I stay in hotels a lot because of my job. I don't normally tip the housekeeper, unless they bring me extra soap, towels, etc. I think the practice of tipping the housekeeper is going by the wayside...I only know one person that does it out of all of the road warriors that I know. I do tip the bell staff, if I use them, but I generally carry my own bags to the room. I always tip room service, and usually about 20% (unless it is an automatic add-on to the bill).
I give holiday gifts instead of tips. Until recently, I had a housekeeper. She really enjoyed the smoked salmon that I gave her every year.