I hate to bash someone who is sending legitimate referrals to my pages, and a lot of them, but StumbleUpon may be unfairly represented by Awstats as sending a lot more referrals to your page than you realize.
Each stumbleupon referral will be seen as 5x or so hits in quick succession, rather than just one. This means that Awstats will incorrectly total the number of referrals from the stumbleupon domain.
As far as I have seen, stumbleupon is the only site that does this, I’m wondering if this is part of the technology or if it’s actually spam to try and increase stumbleupon’s profile.