Wow, I guess thats why StumbleUpon is now charging $0.05 to buy users to stumble on your site. If you are ever planning on buying stumbles or trading stumbles visit my forum http://www.seo-bb.com its a stumble exchange forum. We have a 1:1 ratio for trading stumbles there. People that have listed there sites have at least received 15 stumbles.
875000 users not bad money then. PErsonally cannot see the point they lucky. People usually tell each other via email and word of mouth of sites.