I'm a noob so this might be a known issue. I installed RC1 and RC2 on a laptop using a single EXT4 partition. I powered the PC down without shutting down (which I knew I shouldn't have done). On reboot, it starts to boot Android then kicks me out to the reboot screen over and over. I saw in the log display it couldn't mount the drive read/write so, I figured it was a dirty EXT4 partition. I booted a different Linux, use fsck to fix the partition and then everything was fine again.
So, the summary is that a dirty EXT4 partition prevents booting. Looks like there's no attempt to clean it during boot.