No, the answer is not "every restaurant listed". I am aware that many places on restaurant.com are of questionable quality. That's a given.
However, my question is about places which make using the gift certificates a hassle.
 the GC doesn't mention presenting it before you order, and when you present it at bill time, they make a big stink about it
 you present the GC when you order, then they prevent you from ordering many items which are NOT specials
 they stop accepting the GC's, but keep listing themselves on restaurant.com month after month
 their GCs are always sold out
 you present the GC when you order, then they reduce the size of your dishes
 any other situation where they try to put extra restrictions or conditions on you other than what is stated on the GC
Ones I've come across:
 (not on restaurant.com specifically, but with other coupons) Garden Fresh & Cafe Mazeh in Mountain View
 Nha Toi in San Jose (mentioned on yelp)
 Bui in Berkeley (mentioned a while ago on chowhound)
 Rokko in Sunnyvale, Layang Layang in Cupertino
 Garden Fresh again (required payment in cash)
(I would give an example for , because I read it on yelp recently, but I can't find it right now.)