It is only jailbroken using the same exploits as 4.2.1, so not really a big surprise. Apple don't often close holes until the GM release anyway.
Untethering is still a serious undertaking for developers. It is unlikely we will see a new untether before 4.3 is gold as it would completely waste an exploit, which as we know are getting harder and harder to find.
I believe the best we can hope for in the interim is improvement of the backup-plan using 4.2b3 blobs. Anything else seems unlikely in the short term now IMHO.