Richard Stallman, the creator of the GNU Project and a leader of the Free Software Foundation, recently called Ubuntu spyware.
He made that claim because the latest version of Ubuntu (12.10) sends desktop search information to Canonical (the makers of Ubuntu) so they can show you customized Amazon ads directly in Ubuntu's program called Dash. His exact explanation was "Ubuntu, a widely used and influential GNU/Linux distribution, has installed surveillance code. When the user searches her own local files for a string using the Ubuntu desktop, Ubuntu sends that string to one of Canonical’s servers. (Canonical is the company that develops Ubuntu.)"
Stallman's issue isn't the advertising but rather the monitoring and surveillance done by Canonical to provide targeted advertising (as part of the core operating system). I do want to remind Windows 8 users that many of their built-in apps also come bundled with advertising but in the case of Windows, these aren't core components and you can easily skip using them.
Canonical has a built in switch to allow users to turn this surveillance off but most don't realize it's there. I believe a clear question should be asked during the installation (or update) about this and the switch can then be set to on or off depending on the users explicit response.
What is dash? In Ubuntu, the Dash has always let you search your computer for your files, photos and videos. But now it does more than just search your computer - it can search all your online accounts too. So, once you’ve saved the login details in the ‘Online Accounts’ function, you can expect to see your Flickr photos, Google Drive documents and more in your search results, alongside the files on your computer.