I just can't see camping anywhere really close to the house. I think the closest we've ever gone was about 50 minutes from home, but we usually camp anywhere from 1.5 to 3 hours away.
There really isn't anything too exciting to explore within a half hour, that we haven't already visited many times. There is a state park 20 minutes away, and we often go there to hike or bike ride, but not camp.
We managed to get out 20 nights this past season, which was a good usage for us. We camped in DE, NJ, PA and CT. Our typical trip is 3 nights from Thursday through Sunday. The CGs are usually fairly empty until late Friday night when the weekenders come in.