PulseAudio has been found in major Linux distributions like Ubuntu going back to 2008, but it was only in September of 2011 that they hit the 1.0 status. Their next major release is now PulseAudio 2.0.
PulseAudio 2.0 introduces support for alternate sample rates, echo cancellation (WebRTC canceller, AGC), fixed Hurd operating system support, A2DP decoder quality improvements, headphone / microphone jack detection support, virtual sound sink support, and Xen para-virtualized audio sink. PulseAudio 2.0 also completely drops ESounD support while there's now an optional dependency on the webrtc-audio-processing library in order to benefit from the improved echo canceller.
Moving forward, the PulseAudio developers plan to push out major releases every four months. These major releases will be numbered N.0 (e.g. PulseAudio 1.0, 2.0, 3.0 ...) and there will likely be a few release candidates per cycle. The developers also plan for "World domination is targeted for December 2012 ."
Details on these PulseAudio release plans can be found on their FreeDesktop.org Wiki.
Being released today is the first release candidate for PulseAudio 2.0, which is tagged as PulseAudio 1.99.1. The announcement for this first PulseAudio 2.0 development release can be found on their mailing list.