At first, I wasn't sure about the Tumblr Dashboard. Why would a blogging site re-implement a feed reader as an internal service? Why would I want my blogging software to encourage me to repeat other people, to be less original?
But as I started following more people, cool stuff started showing up there: beautiful random things I would never have seen otherwise; awesome links and quotes that were right up my alley. Heck, even just now opening up my Dashboard to grab the url for this post, I found and reblogged this story about last.fm handing over listener data to the RIAA, something right smack in the middle of my interests.
I even started wishing the Dashboard was richer. Why doesn't it recommend additional people for me to follow? Why doesn't it tell me who reblogs the things I post?
Built with the Google AJAX Search API, rtumblr is a one-page mashup that helps you find out who's reblogging you. You simply enter your tumblr subdomain and it'll give you a full list of which tumblr users have reblogged your posts along with links to each of their rebloggings. For example, here's the (somewhat skimpy) list of who's reblogged idfdz.tumblr.com. (Pro tip: it works with tumblrs with their own domains as well, just type your full domain name in the box; example: who's reblogged kungfugrippe.com)
In the meantime, if you like rtumblr (or if you enjoy strange rube goldbergian mechanisms, stuff that glows, or pessimism about the state online music), follow me on Tumblr: idfdz.tumblr.com.