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.
Although I use Pinboard primarily as my Twitter-scraper, its paid annual subscription plan keeps a deep archive of every URL I push into Pintobard. I see beyond the link and into the the content and several levels of sub-links and resources. Every link that has been cached is displayed with a small check mark. If that link disappears in the future, Pinboard still has the content. Just click on the little checkmark to get the cached version of the page.
Pinboard's paid service also enables full text searching. The text search is blisteringly fast, burrowing into content of the linked sources, not just the tags and notes for links.
I'm over on Pinboard.in/topgold if you want to glance at the kinds of things I'm saving, tagging and pinning to a deep archive in my work as the senior creative multimedia lecturer at the Limerick School of Art & Design.