What the hell are you talking about?? Ofcource 3DMark meens something!!! If I know that my system right now makes 8000 at 3Dmark and after I install something or switch drivers or whatever, I get 6000, then obviously something is wrong!! Yes, 3DMark isn't very reliable in comparing different systems with different video cards (they cheat with their drivers like NVidia did back in the FXdays) but for exactly the same system, it's a good bech.
The 8800 GTX scores around 12k-14k depending on OC and the HD 2900XT scores a lot more and which graphics card wins at the end of the day? If you said the 8800 GTX then your right in both DX9 & DX10. Thing that can affect your score (1) G-card drivers (2) OC'ing (3) luck of the draw (4) system config.
Theres too many reasons why one person gets more than the other to make any real comparison. Thats why I care less about 3Dmark scores, I do however care about one benchmark frames per second.
Which one of these benchmarks do you think is the best way of finding out what your system can really do?