For those worried about the issues of content ownership in regards to WordPress.com (as opposed to Facebook and others), here are the relevant sections from the WordPress.com Terms of Service which covers both your copyright protections as well as respect for the copyrights of others:
Section 8: Copyright Infringement and DMCA Policy. As Automattic asks others to respect its intellectual property rights, it respects the intellectual property rights of others. If you believe that material located on or linked to by WordPress.com violates your copyright, you are encouraged to notify Automattic in accordance with Automattic’s Digital Millennium Copyright Act (“DMCA”) Policy. Automattic will respond to all such notices, including as required or appropriate by removing the infringing material or disabling all links to the infringing material. Automattic will terminate a visitor’s access to and use of the Website if, under appropriate circumstances, the visitor is determined to be a repeat infringer of the copyrights or other intellectual property rights of Automattic or others. In the case of such termination, Automattic will have no obligation to provide a refund of any amounts previously paid to Automattic.
…By submitting Content to Automattic for inclusion on your Website, you grant Automattic a world-wide, royalty-free, and non-exclusive license to reproduce, modify, adapt and publish the Content solely for the purpose of displaying, distributing and promoting your blog. If you delete Content, Automattic will use reasonable efforts to remove it from the Website, but you acknowledge that caching or references to the Content may not be made immediately unavailable.