A couple of folks asked how tweetrad.io works behind the scenes (http://news.ycombinator.com/item?id=920610). Here's a little write-up on our technology and some of the choices we made while developing it.
> We also found that OS X’s say command provided somewhat more natural sounding voices. Our solution was to run the conversion processes on a cluster of several OS X boxes running at our homes.
That is awesome! If you ever want to free up those OS X boxes I recommend a couple of Mac Minis hosted at http://www.macminicolo.net/
