Blender 3D: Noob to Pro/Blender 2.5x Interface< Blender 3D: Noob to Pro
This is the revised interface in Blender 2.5x. If Blender 2.49 looks like something out of Star Trek, then the new Blender must be Star Trek: The Next Generation!
The major interface revision was initially resisted by many experienced blender users; but it has turned out that noobs are able to find things easier. The updates have also brought it much closer to on par with mainstream 3D content creation suites.
For the rationale behind the redesign, read this.