Went to Panara the other night, as it's a nice place to eat, good food, and not horribly expensive. Much of the time, they'll have a line halfway to the door, and they keep it moving quickly & you can order within 5 min. This evening, we walked right up & got in line behind the guy currently finishing his order. Apparently, there was something not working right in the computer with the guy's order, and it took a while. A long while. This was the only register with someone at it, but it was obvious that the one next to it was set up to run (it had a total from the last sale, while the 3rd one said "closed"). We probably stood there longer than 5 minutes while FIVE managers & people stood around gawking at the screen where they were having troubles.
After a while, I turned to my wife & asked her (not loudly, but not whispering either) if she would like to go get some mexican. She said sure, and we walked. I'll probably still go back sometime, but I'm not going to put up with being ignored & waiting forever while people stand around.
Also, every friday night my wife & I join a friend of ours for dinner, usually at the Pizza Hut. We had about a month & a half streak going where they would always screw up something with our order (bring out the pizza and it's obvious the cheese formed a bubble & blew up in the oven, leaving a near-bare pizza crust), or be really slow. We rarely had to say anything - they know us and try to give good service in general, but things just kept happening. They always gave us 50-100% off the bill (after which we tipped), and came back the next time.
Almost didn't, though, when one week we were seated and left to sit without seeing anyone for 20-30 minutes (we didn't notice how long it'd been cuz we were talking, but once we paused & realized how long it'd been...) No drink order, no nothing. BTW, we were probably one of five tables in the place with anyone sitting at them. We walked.
My thoughts: be polite, but to the point when complaining, and don't make demands unless it's something simple like a clean spoon. Don't be afraid to walk.