“The “dev4” version covers all the betas and yesterday’s 6.0 GM seed. There are some remaining issues with Cydia and fundamental modules like PreferenceLoader, so it remains an openssh-style developer-only release only for now!”
Yeah, you’re going to want to keep in mind that this version of RedSn0w will not install Cydia for you. And even if you manually installed it, a lot of packages and things are still broken.
The good news here is that it appears that the Dev Team is continuing to make progress with iOS 6. But there are obviously still many hurdles to clear. For example, right now, only A4 devices can be jailbroken. And things like an untether, and support for A5, and A6 devices are still unknown.