...our program policies strictly prohibit any means of artificially generating ad impressions or clicks, including third-party services such as paid-to-click, paid-to-surf, auto-surf, and click-exchange programs. These programs offer incentives for users to view web pages or click on ads, resulting in activity that is harmful to our advertisers.
We occasionally receive questions from publishers interested in using traffic exchanges to bring traffic to their site. While these services may help advertise your site, we don't recommend using them, as they may also result in similar invalid activity.
Members who have since contributed to the Google Groups discussion agree that traffic is good, as long as it doesn't encourage clicking ads. An owner of a traffic program also contributes to say that there are traffic exchange programs that do not condone clicking ads (although there are some that do). He requests that Google not serve ads on pages if advertised in an exchange. I do not know how practical that is for Google because they may not necessarily know if sites are involved in a traffic exchange program, just like they do not necessarily know if users are selling or buying paid links.
However, I think that his last concern is legitimate:
While there are some people who are out to cheat the system, most people are just looking to get more visitors to their blogs. I don't think it's right to penalize people for advertising their website.
I should also note that this should not be overly confused with social media services such as Digg. A recent study on the impact of high traffic due to social networks and AdSense showed that there are few, if any, clicks during a traffic spike as a result of these services:
Here's the thing about trying to monetize your digg traffic: don't bother. There is literally no point. Your best possible bet at getting money out of a digg article is by using Adsense. We've tried on a few of our articles, to test and see how the traffic might convert, and have seen absolutely nothing but dismal results. At best, you can probably expect to make about 1/2 a cent per digg.
Google is checking the Google Groups thread for feedback, so if you have anything to add, feel free to join in on the discussion.
Related articles: How Digg Traffic Impacts Your Google AdSense Account, Is StumbleUpon Considered Auto-Surf Traffic and Against AdSense TOS?, Encouraging Clicks of AdSense Referral Products is Allowed, and How Digg Affects Your Google AdSense CTR and Earnings