I've been a Stumbleupon user for most of it's history. But it lost me a couple of years ago, when it's ham-handed attempt to monetize it's users effectively killed it for me. Seeing an ad every fourth site or so was very disappointing, and seeing the same sites' ads rotate up every 12-16 stumbles quickly became frustrating. My pain was eased somewhat when I realized I could site-block ads that appeared too often, but when SU removed that ability recently I knew I was done with them. Obviously too many fellow Stumblers had 'stumbled' upon this tactic for SU to allow it to continue, and that meant the writing was on the wall. I'll try Mix.com, because I really enjoyed SU in it's early days. But I'm a user not a resource, and if I get treated like the latter I'm gone again.