Cash Back Providers Worth It?

I am kicking myself as I have spent well over 1k at the market this month but yet to use a cashback website. I recall a post a while ago with people complaining purhases not showing and money not getting payed out so I thought its not worth the hassle. I have been on a bit of a shopping spree this year (just added up over 3k @ the market alone) so again thinking I have failed as a cheapie member. I also often stay in hotels but usally book with hotels direct. Anyone had good experience with cashback sites? Also best way to book hotels with cashback and good prices?