Using either the proprietary Catalyst driver or the open-source stack with this graphics card is not a problem on Linux. The ATI Catalyst driver has supported the Radeon HD 4650 graphics card going back many months now and this driver continues to be refined on a monthly basis. When it comes to the open-source stack and the RV730PRO, AtomBIOS-assisted mode-setting has been available for this graphics card since it has been available on the market. There is X-Video and EXA (2D) acceleration support for this graphics card when using the latest xf86-video-ati or xf86-video-radeonhd driver along with the latest DRM code (currently it's not in a release kernel but should be with the Linux 2.6.30 kernel). Fortunately, this updated open-source stack will be present in Ubuntu 9.04. With all of that said, this graphics card is certainly compatible with Linux whether you use the closed-source Catalyst driver or the open-source stack. The open-source stack does not yet support 3D / OpenGL acceleration for the R600/700 series, but we will hopefully begin seeing that support very soon.
In regards to the video playback capabilities of this graphics card -- since fan-less graphics cards are quite popular for media centers -- the ATI Linux stack is not yet at a pleasant state for video purposes. The open-source and Catalyst drivers do provide X-Video support but that is virtually useless for offloading the playback work to the GPU. The Catalyst driver does support XvMC, which is a bit more useful but still not very beneficial these days considering the speed of modern CPUs, but what AMD really needs to do is properly introduce XvBA. As we have exclusively shared, AMD has been working on a new Linux video API known as X-Video Bitstream Acceleration, which will be their answer to expose UVD2 capabilities on Linux and to compete with NVIDIA's VDPAU. The only problem is that while the Catalyst Linux drivers going back to Q4'08 have supported XvBA, AMD has yet to release the documentation to XvBA or push support for this video API into any multimedia applications, thereby making it useless.
Hopefully we will see XvBA be properly introduced by AMD in the coming months so that these fan-less ATI graphics cards will make good HTPC solutions. In regards to open-source video improvements, once the ATI Gallium3D driver is in a functioning state later this year, we could see a VDPAU implementation in Gallium3D, another video decoding interface, or generic GPU decoding using shaders.
We do not have the PowerColor SCS3 Radeon HD 4650 512MB test results to deliver today, but they will be available in the near future. In regards to the pricing for this passively-cooled Radeon HD 4650, the retail version can be purchased for under $70 USD.
For more information and pricing on ATI graphics cards, visit TestFreaks.com.