Two things stand out here. Google is apparently quite interested in online casual gaming companies. TechCrunch states that Google invested around 100-200 million USD in Zynga, the company behind things like
SpamVille FarmVille and Mafia Wars, immensely crappy but extremely popular games on FaceBook.
Google went a step further with the other social company; they simply flat-out bought Slide. Slide makes a lot of stuff for a lot of social networks, and it's all things I'd rather steer clear from. Still, the products these companies deliver are very popular, and as such, it makes sense for Google to invest in them.
Furthermore, Google also announced that the Google Chrome Web Store will open in October. Good news: Google will only take 5% of the revenue (a processing fee). This means Google isn't looking to monetise on the Web Store. Possible bad news: advertisements all over the place?