EDIT: 4th round: http://lists.blender.org/pipermail/bf-blender-cvs/2009-May/019320.html
And all this will be in 2.49. If you want to describe it, you can say the speedups are incredible, unprecedented, exciting, amazing, jaw dropping, ect...
2.46, 2.48, and 2.49 are on track to be the biggest releases for the BGE in the history it has been in Blender.
2.46 - Many bug fixes and the elimination of the BGE's crippling memory leaks
2.48 - GLSL, logic enhancements (bricks and python)
2.49 - Python API update, all the performance enhances mentioned in the links above, the two mailing list links about enhancements not found in the BA thread.
Enjoy your now to be much faster BGE, grab a build at graphicall.org if you don't want to wait till 2.49.