I'm curious on how to do that? I'm guessing you add another field and wait for the user to log in and if it matches, you salt and hash the new password field with the new function.
Links from people I follow on Twitter would be a killer feature, as would 'links I have already followed' from Twitter.
It seems kinda hard to imagine that a one-time $9.58 fee can really cover costs and leave some living expenses left over.
Also keep in mind Pinboard's optional $25/year fee for archiving copies of your bookmarked pages.
Like auto-adjusting keywords for typos? ;)