The official RSS feed seems to only support 'favorites' which is a specific playlist, unlike 'likes' (http://www.youtube.com/my_liked_videos) which is where a video is collected once you click the 'thumbs up' icon during or after playback.
It was brought up with the Google Data API team over a year ago, but hasn't seen much discussion/action since: http://code.google.com/p/gdata-issues/issues/detail?id=2345
Best Answer
http://gdata.youtube.com/feeds/api/playlists/
now, at the end of that URL you add the playlist code at the end of your likes URL (go to likes and play some vids in the list...)
http://www.youtube.com/watch?v=1TM-3D9F8Bw&list=thisistheplaylist-codeyouneed
just remember to get the whole code, normally, a favorites or other playlist code is one string of alphanumeric digits, with your favorites, it is 2 strings separated by a dash.