MuscleNerd has successfully jailbroken iOS 4.2.1 using the SHSH blobs from 4.1, instead of 4.2b3. The existing method proved to be problematic because only developers have access to iOS 4.2b3, leading to piracy concerns. Using the blobs from iOS 4.1 — which is freely available to all OS X and Windows users — is much easier for users, and less worrying for the Dev-Team. A new redsn0w beta implementing this new method should be rolling out shortly.
Ported Monte back to 4.1 kernel (SHSH blobs). Next step: porting it forward to 4.3beta!