Well here goes.
Ati Linux Driver Issues:
1) Performance/frame-rate.
2) Existance of -Critical- bugs in production releases.
3) Mysterious/lack-of-output installer.
4) Lack of Functional and Easy to Use Control Panel
5) Lack of documention for...pretty much everything.
6) Driver chokes if more than 1 ati card is installed (crossfire or not).
7) No crossfire support.
8) Many releases, but mixed-progress. Not proving helpful.
Nvidia Linux Driver Issues:
1) Lack of power-saving options for mobile users.
2) Not open w/ community regarding 'when' releases will be.
3) Lack of RPM packages (w/ the exception of Redhat users

) for distribution management.
4) Lack of Xorg 7.1 support.
5) Poor SLI performance.
6) Limited FreeBSD version support.
Examplantion for Ati points above:
1) Well this is a no brainer. Nvidia drivers are on-par w/ their windows counterparts in most instances.
2) Bugs exist such as only 1 x-server at a time, or an entire product line does not function. [example: Attempting to use 3D applications on Radeon 9000/9100/9200/9250 and FireGL 8x00 products fails to start and reports back something similar to ?[fglrx] API ERROR: could not register entrypoint for SelectTextureSGIS?. Further details can be found in topic number ]
3) The installer will say "completed successfully" even if it did NOT complete successfully. The gui is nice, but all of the functionality one would -expect- in an installer is lacking.
4) This is a no brainer. We've seen the FireGL Panel for years. Lets get a real config utility already! One that at least offers configuration of various features etc. without interruption of the x-server, and that provides info such as Temperature, FSAA configurations, etc.
5) All of the Xorg.conf options, how to accomplish certain tasks, etc.
The README has no documentation on any of that. The FAQ is pointless (very outdated and inaccurate) and of course, when to use Aticonfig over when to use xorg.conf editing. What are the recommended best practices?
Nvidia's Readme is VERY SPECIFIC for every feature. Ati does not provide any such documentation. They sure show a lot of pictures of their installer though.

Also, any limitations seem to be "hidden". (i.e. it requires Xorg 6.9 or higher to get TV-out to work w/ X1000 series cards. I don't see anything anywhere referrencing which Xorg/Xfree version you need to get which features to work).
6) Some of us actually have more than 1 card in our desktops. God forbit right? Nvidia can drive multiple cards w/ no problems. Ati can't. You have to physically remove the card. Of course when you're under a SLA with a vendor, they often don't let you do that! So ati has no solution to this problem.
7) For the hardcore gamers that dual-boot, this would be nice. Some users have a crossfire rig (it's true). IF they want to dual-boot into Linux, they have to remove one of the cards! At least with nvidia, you don't have to do any hardware modifications, you just reboot normally. (granted their SLI performance is lacking, but the fact that SLI seems stable and at least works is a good starting point).
8) Once again, releasing all the time is great, but introducing serious/critical bugs into a Production Release? Maybe Ati is not using the correct approach here...?
Explanations for Nvidia Points Above:
1) Ati has been generous enough to give users the ability to utilize the predefined clocks of Powerplay. Nvidia still lacks PowerMizer functionality w/ their linux drivers. Would be nice for mobile users who are trying to get usable battery life in Linux!
2) You may know that a bug-fix is coming in the next release of the nvidia driver (by emailing them), but they won't tell you when that is. In some cases, that could be 4 months! Need to be more open/honest with the community regarding the 'WHEN' component of their release cycle. If not for all releases, at least give rough estimates for their 'next' driver (releasing sooner than announced isn't bad either!)
3) I will say this has been a strong point for ATI. They have distro-specific builds. While the nvidia installer seems to be universal, it sucks from a package-dependency management point of view. Perhaps taking an approach similar to Ati for various distributions would allow better package management for end-users? (I noticed various RedHat folks get an Rpm, what about us SuSE guys?).
4) While xorg 7.1 is still not in any fully-released kernels, I will say that it can't hurt for Nvidia to keep ahead of the game by at least trying to keep people happy. Ati has surprising done this (although w/ some big bugs). Would love to hear an explanation as to 'why' they are holding back.
5) This is a no-brainer. SLI profiles don't seem to readily exist for Linux. Granted this may be due to the fewer number of games, but perhaps we could see the 'roadmap' or at least a 'rough idea' of what to expect from SLI in linux in the future?
6) First off, the fact that Nvidia supports FreeBSD is a Huge deal as Ati does not. So this issue can't be held comparitively against ATI. That said, Nvidia keeps discontinuing support for older BSD kernels every other release, forcing users to upgrade. Some people prefer the Legacy 4.x BSD releases for stability reasons. Would be nice to perhaps see a 'legacy' driver for BSD users!
That's all I got. Quite a bit of reading, sorry
