Stumble and Digg are both fine.. This question has been asked dozens of times, and someone will always chime it and say "it's against the TOS, you'll get banned" - yet everytime I asked them to point us to the part of the TOS that says this, they fall silent.. I've been on the front page of Digg twice resulting in about 100,000 visitors in a week.. and since then, for over a year and a half, I've gotten 500 - 1000 visitors from those stories EVERY DAY.. I've had several Stumble-Storms of 3,000-5,000 visitors and many other smaller ones.. No problems.. FWIW - Digg users and stumble users do not convert well with adsense.
What about donkeymails and PTC sites like adbux and so ? They all fine .. ? they pay users to click there , well the advertiser pay users to click , right so its all fine ..
I had almost nothing (clicks) all day yesterday and was worried I got shut down, today clicks are back, I looked at Analytics for yesterday, five times normal traffic through Stumble rush but no normal clicks all day. What happened to normal clicks. I can see Stumblers stumbling through without clicks, but my normal clicks were 10 % of a normal day... Hmmm.