I'm wondering who needs a bookmarking app in 2013, let alone pay for it.
But yeah pay for one... you'd have to have a special need to pay for one. For reference the one I have been using and enjoy is Kippt (https://kippt.com)
HOWEVER their latest update has broken login on Safari if someone from kippt reads this please please fix it so I can use it on my ipad :)
Perhaps there is a use case outside mine? I also don't give an iota of a shit about socially sharing my bookmarks.