Three times in recent memory.

Once was with Mr. LabCat at a local restaurant outside DC, noted for good fried chicken (which he had a craving for). Walked in and were told by the hostess to take a seat anywhere but she didn't give us menus. The place was about a third full. We waited. And waited. And waited. The only place the wait staff seemed to be paying any attention to was the bar area. We waved and got a nod from a waiter as he walked by with food for a table in the bar but he didn't come back. After about 15 minutes of being ignored, we walked out and went to our favorite Thai place instead. Won't be back.

The other two times happened on the same night in NYC. A group of five of us had reservations at a small Italian place at 8:00. Before dinner, we stopped at a different place for drinks. You'd have thought we were invisible. No amount of gesturing or calling out made any difference. One of my friends even tried waving a $20 bill to see if that would lure anyone in. Nope. They apparently didn't want our money so we left. Won't be back.

We got to the restaurant where we had the reservation a little before 8:00. The place was small, with just a tiny bar that could seat four or so people, and every table was full. No room at the bar either and there wasn't really a waiting area, so we stood near the door and shared a bottle of wine while we waited. Come 8:20 or so there was no indication that any of the tables would be clearing out soon. The manager was very apologetic, saying that the party at our table was taking much longer than expected. By 8:30 we decided to leave and try our luck elsewhere. The manager comped us the wine and apologized profusely. I'll definitely try to go back to that place next time I'm there, not only because it looked great but the staff were fantastic to us.