Staples isn't too bad. Concidering all the instant coupons people used to get stuff cheap, and their price matching policy, I'd say the rebates are just more sugar to an already sweet deal.
Anyways, I'm 2 for 2 on staples rebates processed by them. Look out for them in the mail, they look like a personal check that they just wrote your address on it. I was lucky to find mine with the rest of the letters, but usually they end up in the junk mail or in magazines.