From what I've read it can be okay in *small* quanities. Generally it is much better to feed your dog dog-food as it has been designed to meet its nutritional requirements.
I usually have a " slop jar " of things I haven't eaten.... just a few veggies etc and any water left over from cooked veggies, rice etc. I always moisten Chip's kibble and would rather he has the vitamins than the garbage disposal .
It's not bad as long as you aren't feeding them junk. My dogs will get some left over meat and veggies mixed in with rice. Ofcourse that is on the rare occasions I cook (and on the even rarer occasions there even IS any left overs).
