Maybe you thought about it as well, the implications of using Facebook and/or Google+, and the decision differences between the two.
You have a problem with both even if you decide not to use them: People will still add you to those networks. Anyone of your friends, or even people you only had contact with once, who added you as a contact in whatever (email) platform can use the friend finder or import their contacts, or any other Facebook app pushing your data into Facebook, and at least some of your data will be stored on Facebooks servers. Same with Google. Most Android users will synchronize their contacts with Google for backup, maybe Google+, and especially GMail. Do you have any friends with an Android phone?
Your data is already on their servers. So, does not using them make a difference?
Absolutely. Especially with Facebook, they will only have general data about your person, not behavioural, preferential or interest data. If you use Facebook, even with the Facebook Platform (3rd party apps you can use, with potential evil EULAs and/or doings and data synchronizations) disabled, when youâ€™re using the Like button or share links or text via your status you will give that information to them. Even worse, with Like Buttons on any website Facebook could, can or does track which websites you are surfing and how long you stay and navigate on them. With Google, maybe you already provide behavioural data via other Google services like Google-Mail, Google Reader, Google Docs, Google Maps or even searching? Still, using Google+ will be another step, linking you to other people and potentially sharing even more.
Personally, I know my data is already with Google. Also, they are big, have been running longer and they are not only based in the US but also in Europe, which makes it less probably they will misuse your data. They will at least have to follow EU data protection rules and public opinion. Not so much with Facebook. I also think to know way better what Google uses the data for over Facebook. Google has been using data for their adverts system. Facebook, although worth much in the stock market does not gain earnings yet if I remember correctly.
Furthermore, visibility management is way easier in Google+. Also, AFAIK, with Google+ 3rd apps (which there are non yet) can not get friends data as easily or at all, like with Facebook. Your friend is using a malicious 3rd party app? Your data is shared as well.
In the end, personally, Iâ€™m much more comfortable using Google+.
Now, all those principles will have to be prioritized and weighted by you.