Recently returned from 3+ weeks in Italy and reserved all of my restaurant reservations.
I used Quandoo for one or possibly two reservations, one was a pretty classy restaurant on a hill in Trastevere Rome. I seem to remember thinking that the one I made with Quandoo was pretty sketchy and I had difficult getting back on and changing the date when I needed to do that and I wasn't ever sure that the change had been made. I wondered why they were using a third party site like that. The website was really confusing but in the end our reservation was there and all was fine and my changes went through.
Most of my reservations (that I did not make directly with the restaurant) were made with The Fork and I think I made a half dozen or even more with them. All went very smoothly and honored...