Own sync adapter for Android?
These two articles by Sam Steele (January 23rd, 2010) are about the implementation of the last.fm sync adapter. Do not miss the second part and the opensource projects that are mentioned at the end of the articles.
This article, http://ericmiles.wordpress.com/2010/09/22/connecting-the-dots-with-android-syncadapter/, is a great, albeit brief overview of creating a sync adapter and getting it to play nice within the Android framework.
Simple basic explanation by Adam Pullen (last updated May 13, 2011). The article consists of two parts and contains the ShowMyAccountAuthenticator example project.