We try to aim for eating out once a week, mainly so we can have a break from cooking, but also as sort of a date night. Since I've been dealing with some serious health issues for the past 9mo, I'm usually too exhausted at the end of the day to cook, so recently, we've been eating out more like 2-3x a week. We usually end up eating lunch out on Saturday because we've run out of groceries by then and we're sick of any leftovers we have. We usually grab a quick lunch out before we start our weekly grocery shopping.
Recently, we've been hitting a lot of chains that are a step up from fast food, but still quick and inexpensive (Noodles, Potbelly's, California Tortilla). We never do any of the typical fast food (McD, BK, Taco Bell, etc.). When eating out was just a once a week occurance, we'd tend to go to nicer sit-down restaurants, mostly Japanese or Mexican for our date nights. The area we live in currently has a really disappointing selection of restaurants though.
We only get take-out maybe once a month or less. It's always either pizza or Chinese.