How much do you usually tip?

[MAL_ONE]

Ok, here is an update on the tipping thing. The wife and I go to one of
our favorite restaraunts for lunch. While we were there, the waitress
politely ask if we need anything else. "As a matter of fact," I said. "We
could use some more salsa." "No problem" she replied, "I'll be right back
with that." Well, after waiting for a few minutes (glacing around the floor,
she is no where in sight), I finally get up and make my way back to the
kitchen to ask for more salsa, where I observe our waitress busily
talking on the phone.
Question: how much should I tip her now?