I live in DC and find that at least 3/4 of the restaurants listed are 'fair' at best. The other 1/4 are pretty decent for what they are (most are casual restaurants, very few are truly 'fine dining').
Although when I look at the participants in Philly (a city I am familiar with) there are many very good resturants listed.
When travelling, I usually use iDine's list, cross referenced with another restaurant listing. If it shows up on both, then I feel it is probably a good restaurant. Sometimes, tho, I will try an cheaper iDine listing on its own -- if I am disappointed with the food, at least I am not out beaucoup $$$
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Da DOK