Radeon and Radeon HD drivers are getting more mature, but I still don't know if they can handle the advanced graphics that the proprietary drivers can do. Only problem, ATI proprietary drivers are a problem installing in Linux. Depending on what kernel your running and what version driver you need to install. Some folks have good luck installing, some have no luck. One app to install proprietary drivers for Debian and Ubuntu distros is called sgfxi. I hear that it's been having some luck with ATI drivers recently. You can search Techpatterns,com if your interested for download instructions.
If you really want good graphics with Linux, get a Nvidia card to replace the ATi card. Their drivers are easy to install and work perfectly on all my boxes.
Of course, I'm sure their are many other opinions.
I appreciate the info. I heard an interview with Linus about the latest kernel in which he stated, if my bio-memory serves, that ATI had released a large amount of code to the kernel team and it was incorporated in the last release. 2 yrs. ago OpenSUSE just could not run this card correctly, even for basic video; but 3 wks. ago Ubuntu 9.10 runs all perfectly. I figured it was due to the code to which Linus referred.
Nevertheless, I keep reading, here and elsewhere, that Nvidia, generally, is the most Linux friendly, which matches what I read 2 yrs. ago. I have been experiencing difficulty getting reliable info on this matter, although I'm sure that my vague understanding of graphics lingo is not helping me to decipher what I do find.