Breaking news: a huge advertising company would like you to give them as much of your personal information as possible and encourages you to use their services more frequently, for more reasons, and for longer durations each time so they can show you more ads and make more money from the advertisers.
Exactly. Although I do use Facebook and Twitter, I do worry about privacy and where my information might end up. Not too sure I want Google knowing more about me than it already knows, especially because, as Marco suggests, they'll probably use it to show me more ads anyway, which has absolutely no benefit to me.
If you want to be surprised at how much Google already knows about you, log into a Google service (Gmail, Reader, or whatever) and then go to Google Dashboard. You'll probably be surprised. Scroll down and look at your browsing history. Google stores that and uses it to target ads to you.
I'm not jumping onto Google+ any time soon. There are already way too many things to keep track of in my life and I definitely don't need another one.