I guess it all depends on how valuable the service is to you. For me, the one-time signup fee seems minimal for the value I get from a service that I use nearly every day. I've used many other bookmarking services, some of which have already disappeared like Gnolia. Pinboard is very stable, faster than Delicious, and the developers respond to requests quickly. I have no connection with Pinboard other than as a happy customer, but I regularly recommend the service and think it is worth paying for.
I use Pinboard to help collect data for many of my research projects and the archiving capability ($25/ year) is great retrieving pages that have already disappeared, that I want to go back and reference. Yes, I could use other free services and the Internet Archive Wayback Machine (which is amazing), but the speed, support, and reliability of Pinboard make it easily worth the cost. I prefer that services I rely on have a sustainable business model. Charging a very reasonable fee to provide quality service seems like a good model to me.
I use Pinboard to help collect data for many of my research projects and the archiving capability ($25/ year) is great retrieving pages that have already disappeared, that I want to go back and reference. Yes, I could use other free services and the Internet Archive Wayback Machine (which is amazing), but the speed, support, and reliability of Pinboard make it easily worth the cost. I prefer that services I rely on have a sustainable business model. Charging a very reasonable fee to provide quality service seems like a good model to me.