There is a new report from Incapsula that shows bot traffic up yet again. (Basically, a lot of web traffic is 'not human'.)
Here is their graph with the results of their research. There is a more detailed on on their blog, linked above.
Adweek had a great article about the amount of 'questionable' traffic that is out there:
And a few weeks ago WSJ had an article that showed how fake or automated twitter traffic works.
Ultimately you have bots filling out forms just to pump more spam out, in addition to comment spam, which is also automated….
The next step will be automated bots that both buy AND sell traffic that they create. Unless someone created a machine to do that already.