But Pinterst showed how the "social" side of "social bookmarking" should really be done.
I remember showing the original del.icio.us to my friends and them all saying "I don't get it." And then I said "instead of emailing everybody links, you can just post them here and we'll all get them automatically" and they went "Ah! Now I get it!"
Edit: Am I wrong?
Meaning, yes you in the past had to share links via email. Delicious solved that with both parties on Delicious.
Or they subscribed in a RSS reader.
With delicious From day one you bookmarklets that worked with anybrowser. And a kickass Mozilla sidebar thingy
Chrome has a nice feature where you can see what tabs you have open on other computers (assuming you are signed in and have sync enabled). I think Firefox has the same, but I don't use it often enough to have looked for it.
You were also, at that point, restricted to arbitrary hierarchies rather than arbitrary tagging. The ability to slice bookmarks over multiple categories is stupidly useful (for me anyway.)
Need something that's cross-platform, cross-browser with arbitrary tagging and suddenly you're looking at third party service.
Add to that the discover side of shared bookmarking tools (Gee - I wonder what everybody else has tagged with "foo") and a third party service is the only thing that will help.
I was a really happy delicious used before the post-yahoo rewrite. Then they lost about 1000 bookmarks of mine so I moved to pinboard - where I'm not quite unhappy enough to go write my perfect system ;-)