I found these 3 posts really useful around controls, generic.xaml, resource dictionaries and error codes for Silverlight 2;
http://marlongrech.wordpress.com/2008/03/19/genericxaml-in-silverlight-beta1-for-wpf-developers/
http://www.codeproject.com/KB/silverlight/mediabutton.aspx
http://exdream.no-ip.info/blog/2007/07/20/SilverlightErrorCodesExplained.aspx