With a Starbucks, a Chipotle, a Tutti Frutti, and now a Potbelly Sandwich Shop, the east side of Charles Street between Biddle and Preston might well be dubbed "corporate corner." Still, to be fair, we had to try out the newcomer to our corporate-restaurant scene. We got an original-size grilled chicken-and-cheddar sandwich on wheat, and an original Mediterranean sandwich with hummus and vegetables ($4.70 each; they also have "skinny" and "big" sizes). Both of the sandwiches were tasty enough; the bread nicely toasted, the ingredients decent; they were fine sandwiches in a pinch. But the thing is, we're not in a pinch. Barely a block away is the locally owned Soup's On (11 W. Preston St.,  528-1003, soupsonbalto.com), which has much better sandwiches for a mere 30 cents more (and soup!), and keeps its profits in the city. So, if you're stuck out in the middle of nowhere, Potbelly rocks. But if you're in the heart of Mount Vernon, you can do much better for yourself and the rest of us.