They're both basically pointless. One GPU will do just fine. I'd rather have a newer $400 card than 2 $200 cards with all of the micro stutter issues. Not to mention the need for a better power supply, as well as cooling.
They both do essentially the same thing.
Both have bridges. segerydrth
The point of Crossfire and SLi is to basically combine the power of the multiple GPUs however
people think that two GPU=2x the power, but in reality it scales horrible.
The more GPU you tack onto the build the less effective it will be the last one will be.
For example GPU1=100% power GPU2=70% GPU3=40% GPU4=20%
So as you can tell you dont get 2x 3x or 4x the power.
The best thing to do instead of busting $$ on 4 GPU is to spend all that on one top of the line GPU.
I need to find a citation on the GPU thing though sorry.