This new release is the result of two big events: Google Summer of Code and Project Orange.
With the Summer of Code, Google has sponsored several Open Source projects and Blender was one of them. Check out the excellent new Fluid Simulator, Inverse Kinematics and Boolean Operations.
Project Orange, if you didn't know already, is an effort headed by Blender creator Ton Roosendaal to create a short movie using only Open Source tools. While the artists are slaving away in the studio, Ton is coding like a madman and creating the tools that they need. Pretty much all the other new stuff is from his hand.
Oh, a word of warning: there's an issue on OS X 10.4.3 and Apple's drivers of Nvidia graphics cards. Word is that 10.4.4 will contain a fix for this. In the mean time, maximising the Blender window sometimes helps.