ATI has responded to NVIDIA's WHQL release of 257.21 drivers by outing Catalyst 10.6 a little earlier than expected.

Head on over to here for the download links, and then zip along to here for the full release notes. Taking out the pertinent sections, ATI notes the following improvements:

New Features
 
GPU acceleration of H.264 video content using Adobe® Flash  Player 10.1
 
AMD GPU acceleration of Adobe® Flash Player 10.1 delivers smooth high  definition video playback and reduces system resource utilization
Adobe Flash Player 10.1 can be accelerated on notebook and desktop platforms  featuring AMD graphics including:
ƒATI Radeon™ HD 5000 and ATI Radeon™ HD 4000 series
ƒATI Mobility  ATI Radeon™ HD 400 series (and higher)
ƒATI Radeon™ HD 3000 series integrated graphics (and higher)
 
Video De-blocking support
 
Reduces blocking artifacts seen in low-bit rate video during playback 
Supported on the ATI Radeon™ HD 5000 Series of products
 
Mosquito noise reduction 
 
Reduces mosquito noise seen in highly compressed progressive video, during  playback
Supported on the ATI Radeon™ HD 5000 Series of products 
 
Official support for OpenGL 4.0 and OpenGL 3.3 
 
ATI Catalyst 10.6 delivers official support for OpenGL 4.0 on the ATI Radeon™ HD 5000 Series
ATI Catalyst 10.6 delivers official support for OpenGL 3.3 on the ATI Radeon™ HD Series

Then there's the usual slew of performance improvements in games such as Alien vs. Predator benchmark; Company of Heroes; Crysis Warhead; DiRT2 DX9, and Wolfentstien.