Just installed the 4.2 beta

[BrennB]

How do I activate screen lock for rotation now?

Excellent question my dear! If it is somewhere in the settings, it must be buried pretty deep because I can't find it (but then again, I never used it!).

double click home to bring up the multitasking bar, then swipe right. the rotation lock control is on there next to the brightness slider and media controls...

Ooooh! I likey!