This came up a few years ago...the thought at the time was to use Latent Semantic Mapping to do this (its the tech that does Spam mail filtering for OS X Mail).
http://developer.apple.com/documenta...an1/lsm.1.html
Should be possible to cobble something together using applescript and the lsm command line tool, but I think that we'll find that just improving the text matching code for entering projects and contexts will yield a more usable end product.