OttoMets is very familiar with Bethesda and agrees with Townie that Louisiana Kitchen makes a good po' boy and some interesting non-sweet beignets; however, most of the restaurants and bars up there are mediocre and are only worth a visit after putting down a lot of drinks during a beer pong tournament at Tommy Joe's.
Seriously, for a place that has so much wealth, Bethesda is a culinary wasteland. Over a hundred restaurants, precious few of which are worth a trip for anyone outside the immediate neighborhood. And, believe me, after working on Montgomery Lane for several years, I've tried all the usual suspects. Black's, Taylor Deli, Vace, Lebanese Taverna, Louisiana Kitchen are good. And a pepperoni/chicken parm slice from Mamma's sounds good right now.
But for anyone staying in the area, the logical advice would be this: run, don't walk, to one of a dozen neighborhoods in the District (probably one of America's best five food cities right now) for a memorable and high-quality meal.