Honeygain–Sell your residential bandwidth
honeygain.com
honeygain.com
I can imagine it's going to be doing lots of false ad clicks on things, scraping news sites, brute forcing captchas, spamming forums, and lots of other shady stuff.
Really wouldn't be surprised if future versions don't 'borrow' your browser cookie jar so they can pretend to be browsing the web with a highly trusted non-spam login to Google/Facebook/etc.
I can imagine this getting your IP blocked from some sites. Chances of you noticing might be slim, but it would be quite a pain if it did affect a site that you do visit.
Also, the unspoken part: They are using your electricity as well. So hopefully whatever you get out of this pays enough for that as well.