All good points of course, and the more honest service providers will tell you the same. In Pinboard's case, the author has regularly joked about being hit by a bus, and how people need to back up their links. He's also got an API in place to enable exactly that.

You could use the same API as a model to reinvent your own personal service, if you so choose. I use it (for now) to just back up everything important, and I'll figure out what to do with the data later if I ever need to.