You betcha it's worth it!
I joined iDine for AAdvantage Rewards Networks AAMiles back in 2006. So far, I have accumulated around 27000 miles by dining.
When my friends ask me where to eat, first thing I do is see where the participating restaurants are. We usually end up at a AAdvantage Dining restaurant. (There's a lot of restaurants in and around Orange County, California.) Then I charge the entire bill (to get the max miles) and get my friends to pay their balance in cash!
Steve