Depends on where I am. In the US it's so cheap to eat out compared to other places that even with a good tip, you're probably still out less money than you would eating somewhere in Europe or UK and not tipping much/at all. And more of the money goes to the actual server instead of "the establishment", as it were. Kind of balances out. But as I said, depends on where I am. In some countries it is seen as rude to tip, in others it's rude not to... so I try to find out the way a place works before I go there.
When I do tip, I tend to tip well, at least 20% usually. I grew up really poor and we occasionally had to rely on welfare or charities, so now that I'm doing well for myself, I feel like paying it forward ^_^