They pop up all over the place around here.
We have one about a mile away that's fairly new.
I'm mixed on it-on one hand we're not particularly far away from proper grocery stores(Schnuck's, Wal-Mart Marketplace, and for the budget mined Aldi and Ruler) and larger general mechandise stores like Wal-Mart and Target are not much further away.
Still, though, the location is convenient. They are an easy walk from several apartments and such in town, and there's really nowhere else in town aside from overpriced stuff at Casey's down the street. They really do serve a valuable purpose, IMO, for people who for whatever reason are unable or unwilling to drive, especially since the larger stores I mentioned would not be an easy walk from here.
At the same time, it seems like their prices have gone way up compared to a few years ago. I use to go to Dollar General or Family Dollar to buy things like wash tubs and the like for the garage. I knew I wasn't getting the best quality stuff, but it was hard to beat for the prices I use to pay. The last time I went in there, I bought 3 18qt wash tubs and they were something like $5 each. My wife looked and found 20 qt. ones at Target for something like $4.50. That's just one example I can think of, but I don't really consider them a place anymore to get a bargain on things like this.
As another side note, about a year ago my wife and I found ourselves staying ovemight in a VERY rural area of Missouri. She'd wanted to visit Marceline, MO for a while, and we took a weekend trip there. There really was not much in the town after they closed up at about 4:00PM on a Saturday, and we ended up driving 30 miles or so for dinner. Across from our hotel, though, was a fairly large "DG Market." We went in there just to walk around and look since, well, there wasn't anything else to do. They had a pretty surprising selection of groceries and such. They weren't CHEAP, but they were certainly better than convenient store prices, which would have been your only other option in the town. I just did a bit of poking around and the closest I could find to anything resembling a "real" grocery store was a Wal-Mart that's 30-something miles away. These "DG Markets" were all over the place, and I imagine they do provide a real service to the people who live in all these little towns.