flickr: pix, tags, sets, groups, comments, rss (small), flash-slideshow (w/#), faves (no sort, no tags, no sets, no ratings), faves-rss, faves-slideshow (w/#); rss/slideshows for artist w/tag, for set, for group; no aggregate feeds; privacy settings?; 3rdparty (flickriver)
twitter: tweets, subscriptions (no privacy re who), one aggregate feed per user, faves (no sort, no tags, no ratings)
imeem:
last.fm:
postsecret:
overheard:
blogger:
tumblr: