Great write-up by Bryan Irace:
The process of building the Tumblr share extension has been fun, but also really frustrating at times. We’ve hit quite a few problems that we ended up needing to work around, and in the interest of helping you do the same, would like to detail all of the issues that we encountered.
Of course, your mileage may vary with some or all of these. We’ve talked to other developers who haven’t had the same problems, or have hit some that we haven’t.
I'd like to see more blog posts like this one.