Pinboard is certainly a niche service but one I depend upon for deep insight and resilient back-up of several Twitterstreams. It's fast, consistently informative and worth the small pocket money I contribute to its ecosystem.
I jumped over to Pinboard at a time when Delicious looked wobbly. Several colleagues migrated to Diigo at the time--I'm happy where I landed because of the network knowledge effect gained as I sift through shared bookmarks. That kind of sifting became impossible after Delicious shifted its look and feel away from a text-first system.