The official change log is as follows:
The third beta is now available (testers ONLY please!). This version extends the fix made in beta2 over to the non-GUI programs too (like the daemons that handle media content). So now embedded videos in iTunes work.
The instructions for untethered jailbreak are exactly same as before. Follow our complete step by step guide posted here to jailbreak (untethered) iPhone 4, iPad and iPod touch 4G on iOS 4.2.1 with Redsn0w 0.9.7.
NOTE: All the standard warnings mentioned previously still applies