Previously to untether your jailbreak using Monte you needed to have the iOS 4.2b3 SHSH blobs saved which was developer only. Now you will only need your iOS 4.1 SHSH blobs. The team is also working on porting Monte forward to iOS 4.3...
Ported Monte back to 4.1 kernel (SHSH blobs). Next step: porting it forward to 4.3beta!
MuscleNerd notes that the beauty of Monte is it doesn't expose any new exploits :) It makes the entire "wait until next FW" concern moot. Think of Monte as a "green" jailbreak. It recycles (for example) 4.1's exact JB exploit on 4.2.1 :) Waste no exploits.
We'll let you know when RedSn0w is updated with the new capabilities.
The Chronic Dev-Team is also packaging up an untether for iOS 4.2.1 that will not require SHSH Blobs.
Stay tuned for more information.