I use OpenTable from time to time. Very handy. And I've redeemed a couple of the $10 dining checks at participating restaurants with no problem.
Don't forgot about the 1,000-point bonuses offered (SF and NYC offer this -- don't know about other cities). Some OpenTable restaurants give you 1,000 points instead of only 100 for booking and dining at off-peak times. Check the website for details.
We should compile a list of restaurants that participate in BOTH OpenTable and idine. I know of one in San Francisco, and it even has the 1,000-point off-peak deal on some days! On second thought, if this information is shared too widely, the "deal" may disappear....
Kathy