I use the FireFox bookmarks thing so it gets added to my bookmarks, but I don't use the Bookmarks thing at the bottom where it shows links to Digg, del.ico.us, StumbleUpon and Google. I only bookmark things sometimes.
I have digged sometime basically releases. I guess we need not to bookmark as Releases are already popular and doesn't require bookmarks. While yeah can be good for Search engine ranking based on keywords