In one mailing list that I follow, there are friends who asked about the share button to make a FB / Twitter on your WordPress blog are paid. This means using a WordPress blog run by web hosting. Then, penginnya each time to post an article then can be shared via Twitter / FB.
In my opinion, there are 2 things in order to share your blog with a FB / Twitter:
1. Using an existing WP themes inherent to the share to social networking. Many koq choice. Examples of my existing blog share button is http://kerjadirumah.web.id
2. For non-WP themes have built the menu page, must install the plugin. Examples of this blog or blog http://way2diamond.com. Plugin which I installed in order to share the posting to twitter is "tweetmeme". As for the share to the FB I've made automatically from twitter.