The LANL Tech Transfer Division has released RaveGrid, an image vectorization and segmentation application. A free version is available (a quick 2.1M download), which is supposedly more limited than the non-commercial and commercial licenses (though I wasn’t able to determine what those limitations were). As far as performance,

On a Pentium 2.13 GHz M processor with 2 GB RAM, this version vectorizes images at an average rate of 0.55 mega pixels per second.

The free alternatives are, of course, potrace and autotrace (and see this comparison).