According to Sidewinder Linden, program manager for the Havok 4 project at Linden Lab, Havok 4 will be rolled out across the whole Second Life grid starting Monday, 31 March (depending on the overall performance of the RC3 update over the weekend). Looks like we win the betting pool, and that means candy!
More than half of simulator crashes and restarts are tied back to physics problems. That being the case, it seems that this new code will be the most stable Second Life simulator ever. According to the timetable, assuming the current release candidate is not found wanting on Monday morning, it will be rolled out to an initial group of up to 2,000 simulators, followed by a deployment to all the rest on Tuesday, 1 April.
We believe you'll also see Windlight (1.19.1) roll out as the official viewer on Monday, or perhaps Tuesday. It's going to be a hell of a start to the new quarter.