Nice little video by what looks like some design students. Really reminds me of the graphic design which was part of the Hitchhiker's guide to the galaxy. Their concern centres on the privacy issues around Google.
This blog is written on Google software, they can see what I search for (personalised search), what I read (Google Reader and Google News), and even what files I look at (Google Desktop). This will translate into a very detailed picture of me.
Google's performance shows that the majority of people are willing to accept services in exchange for a loss of privacy. It is quite impressive how much information Google currently has on me, but I am quite comfortable with that. There have been no examples of Google abusing privacy so far (that I am aware of).
As with all web services, Google are acutely aware that their competition are only one click away. If you even think that there's a small possibility that Google could do something that would make your life worse, you're going to go to the competition. Hopefully Google will keep that in mind when they're being tempted to abuse their data.