The most recent builds I can find are here:

http://people.mozilla.com/~pavlov/fennec/hourly/

the current one is labeled 0.9pre. It's actually quite stable. renders *significantly* faster than MicroB, with near instantaneous zoom. There are still some UI issues, though, many of which relate to the onscreen keyboard. You can tell right now that once this is polished it's going to be much better than microb.