I'm pretty happy with prebeta21 right now.
I noticed the idle pwm voltage correction at cranking like y8s noted, but i didn't notice the "double-dip", only that I needed to dial it back a bit, and reduce the cranking table a little. I had the voltage curve too aggresive at first, as I drop to 9v during cranking. Seems to be fine after a bit of tuning and lowering the cranking duty a bit.
The accel-pump is amazing. I'm currently struggling with an odd grounding issue where my enrichments had to be completely retuned and my tpsDOT was very noisy and required a high threshold. Coming from alpha11, the filtering improvements coupled with the accel-pump have results in the best throttle response and smoothness to date. (consider that I've been on MsI starting in 2006, then MS2, and now MS3).
The idle improvements (intial duty, timing and voltage correction) have improved the idle quality significantly, better than the stock ECU was ever able to.
Here's the results of my idle after about 10-20 minutes of fooling around, going straight off my alpha 11 map.http://www.youtube.com/watch?v=aeSrl9EockA