OpenGL Shading Language was approved in June 2003 by the OpenGL Architecture Review Board (ARB) as an extension to OpenGL 1.4, which has since then been updated to version 1.5. This language was always ment to be integrated into the full OpenGL specification, which happened today.
Next, graphics chip vendors have to offer OpenGL 2.0-capable drivers, allowing programmers to code using the new API in the sure and certain knowledge that their apps will run on the latest programmable pixel and vertex shaders from ATI, Nvidia, Intel and co.Source: The Register
And, indeed, both ATI and Nvidia were quick to voice their happiness that Shading Language has been wrapped into OpenGL and is no longer an optional add-on.
Programmable shader support remains OpenGL 2.0's key feature, but it's not the only one. The ARB have also included technology that enables support from multiple render targets in a single pass and to allow developers to apply rectangular rather than square, 'power of two' textures for all texture targets.
OpenGL 2.0 also adds support for point sprites, "which replace point texture coordinates with texture coordinates interpolated across the point". Essentially, points are treated as textures and textures as points, enabling some interesting particle effects.
The API now includes two-sided stencil support "with the ability to define stencil functionality for the front and back faces of primitives, improving performance of shadow volume and constructive solid geometry rendering algorithms".