We've been very happy with it. I agree that you should make sure it has decent lounges in the places you use most. Last I looked, there were no lounges available at CVG, which would be pretty bad if you flew DL a lot.

I've used them in Zurich, Prague, LHR, Cleveland, ORD and probably some places I've forgotten. There was supposed to be one in DEL but it didn't look like I could get there once I got through the onerous Immigration and security lines (everyone was patted down). If ever I needed an airport lounge, it was DEL. The US lounges were typical since they were the major airlines' lounges- USAir, DL, CO, AA (not all clubs in all cities). UK/European lounges varied in quality and food selection, but no really bad or overcrowded ones.

I bought the $250 plan- it gave me 10 visits and I think I used all or most of them. (They charge after that, and also charge for guests.) Will definitely use them again next year.