To be fair Pinboard.in was down quite a lot recently and its DNS has expired(1).
There was a big discussion here (2) and on Twitter IIRC that the author had lost his interest in product and no updates were being made. So there are no guarantees even when it's paid.
Been pretty rock solid for me for years. Nobody said paying someone the price of a cup of coffee would get you a service with zero hiccups (again: none of which I've experienced, but I believe you). Maybe you should start shaking Maciej and demanding he accept more of your money, or run ads. :)