Radeon HD 2400PRO: The Radeon HD 2400PRO 256MB is the first R600 graphics processor being featured. The R600 graphics processor is architecturally quite different from the R500 GPU and is a bigger leap than the differences between the R300/R400 and R500. Like was the case for previous generation graphics cards, it took several months before there was Catalyst Linux driver support following the product launch. Fortunately, the R600 and newer GPUs are still supported by modern Catalyst releases. However, the Catalyst support though is likely to be dropped within the next 30 months. The Radeon HD 2000 series is effectively feature complete with the Catalyst Linux driver.
The open-source R600 series support did not come until September 2007 when AMD rolled out their open-source strategy. The initial support was in the form of user-space mode-setting via the RadeonHD driver and then ultimately onto 3D support many months later via a classic Mesa driver. Finally, in 2010 the R600 Gallium3D driver was quickly taking shape. The R600 Gallium3D driver is now the default in Mesa and new Linux desktop distribution releases.
The R600 Gallium3D support with the latest Mesa (version 7.11 and 7.12-devel) is nearly as good as the R300 Gallium3D driver, but it still has limitations. The performance comparative to the Catalyst driver is normally not as high as for the older ASICs. There are also the aforementioned R500 series limitations with missing features like CrossFire and UVD video decoding. Additionally, Radeon HD 2000 series hardware supports up to the OpenGL 3.3 specification. Meanwhile, the R600 driver -- and all Mesa / Gallium3D drivers -- are currently handicapped to the OpenGL 2.1 specification. There is work on bringing up OpenGL 3.0 support into the open-source Linux drivers, but it is a big challenge.
We may see OpenGL 3.0 support in the 2012 calendar year for Mesa as most of the work left deals with GL Shading Language 1.30. However, by then the OpenGL 3.0 specification will be about four years old and there is still catching up to do with OpenGL 3.1/3.2/3.3 and then OpenGL 4.0/4.1/4.2. Additionally, it will be in crippled form by default. There is support for some OpenGL functionality like floating-point textures, but it's not enabled in the driver source-code by default nor are any major Linux distribution vendors (aside from Arch Linux) enabling these features. The support is disabled due to patents / intellectual property covering these technologies. It makes open-source graphics drivers a hot big mess. S3 Texture Compression (S3TC) is also only available as an external library that is not packaged in tier-one distributions due to these legal concerns.
It was with the R600 series where Hybrid CrossFire was introduced for conserving power and splitting workloads between an integrated ATI graphics processor on a motherboard and a discrete Radeon graphics processor. It works with the Catalyst driver, but per the previous CrossFire comments, there is little chance of seeing it in the open-source stack.