I stumbled across Yoono a little while ago. It's said to be "A RSS reader/builder integrated into a social bookmarking application based on browser bookmarks" - whatever that means.
It's an add-on for Firefox (and even IE), so I downloaded, installed and played with it for a few days before dismissing it as a bit flashy and pointless. Then one day my computer made a funny little noise, a noise I've never heard it make before - a cartoony sound, nothing distressing, just curious. So I looked around my screen and saw a small glowing button on the Yoono sidebar - it was an IM from my sister.
That blew my mind. I didn't sign into any IM services that I was aware of and here is my sister asking about the holidays. I came to realize that she saw me online via GMail (which I had set up in Yoono, but didn't have GMail open). After that I decided I'd take another look into this little thing, Yoono. I came to realize, aside form keeping you updated on all kinds of social networks it also stores your Firefox bookmarks on a separate Yoono profile page.
I just downloaded and installed Yoono on another computer and it allows you to merge your bookmarks from separate computers.
Yoono has a few other features I haven't played with, but in all I think its a nice little tool, especially for anyone who IM's or wants to keep up with updates to their Myspace, Facebook, Twitter, Flickr or other social network accounts.