They only work at certain restaurants and only Sun-Thurs, so to me that benefit wasn't particularly useful (we stayed at HRH Thurs-Sun nights)... As far as I could tell, Hard Rock Cafe didn't take reservations at all -- but perhaps that was only on Saturday nights... We waited a pretty long time to get into that restaurant even though it was 9:30 pm by the time we arrived!!
I'd definitely recommend getting ressies at places you definitely want to try, even if you're not sure you'll use them... It's worth it!!
Happy trails,
Sarah