After finding out about Google using data from my Android device at least for targeted advertising, I looked for alternative cloudservices and other solutions.
After a short search, I found ownCloud, which is a powerful cloudservice server software, capable of file, contact and calendar syncing and much more. Version 5 is already very powerful and can replace Google contacts, Google calendar and partially Google docs. The upcoming version 6 will additionally include collaborative editing of documents in the Open Document Format which will then be a complete replacement for Google services. All that's needed is a webserver with PHP and a database system, such as mysql. The installation and basic configuration took me about 25 minutes.
In the first step, I moved all my contacts and my calendars from Google to my ownCloud server and deleted the information from Google. As soon as version 6 is out, I will move all remaing stuff away from Google then.
Additionally, I configured some monitoring in my firewall which analyzes traffic which goes from my tablet to any IP address which is registered to Google. Let's see, what we'll find out there...