I'll usually wait up to 10 min to be acknowledged by a server, as long as I'm with others and can kill some time. If I'm dining by myself, I only give it 5 minutes before I start putting up a stink.

As for waiting for meals, the most I'll usually wait is 20-25 min after they've cleared away the previous course. Optimally, I usually like at least 5 min between courses in order to digest/savor. I hate being rushed from course to course because the server completely ignores our dining pace.

(On a side note: I also send back food because it was clear that it'd been sitting in the window too long because the server put in the order too early. I try not to sweat the small stuff, but I won't tolerate soggy/non-crispy fried foods, fallen souffles, gummy/soft creme brulee crusts, meat overcooking under a heat lamp, etc.)