@bwdorsey MicroBlog does not make use of any API keys. It uses your blog RSS feed - which is already publically available for search engines, social media and news aggregators to freely use. In effect, MicroBlog can best be described as being an RSS reader.
The stack simply works to convert the the XML into HTML code. It does a little bit of other trickery to try and detect the types of blog posts and to also markup images, audio and video appropriately for different web browsers to access.
About the only way Tumblr could ever kill-off MicroBlog would be if they were to cease providing public RSS feeds. Which for a blogging platform, would be a crazily stupid thing to do!