I wonder Google wouldnt mind about the traffic AdSense publishers receieved from sites like Stumble upon , digg , del.icio.us etc. ? these are taken as invalid impressions ?
Digg and del.ico.us is legitimate. i never used stumble upon but heard they r categorised as pay-for-surf?? are they?
Stumble upon is not pay-for-surf, as far as I know. These sites can get a lot of traffic and hots to your site, but i dont get why should they be considered as invalid impressions?
Bookmarking is great for traffic, ranking and PR as well. Can you please post link of url where these impressions are said "invalid impressions "