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First of all, thank you so much for taking the time to answer this. It's almost impossible to get in touch with anyone who has tried eyefinity setups in practice.

1) How many monitors do you use? 4? 
 - 3 monitors

2) What brand/model of monitors do you use?
 - 2 Asus 22" , 1 LG 22"

3) Are you using the fglrx (closed) driver?
 - fglrx (catalyst driver) ; catalyst control center software (EYEFINITY options here, afaik)

4) What layout do you use? 2x2, 4x1? 3x2?
 - 3x1 

5) What kind of performance are you seeing? Is everything nice and smooth?
 - all is smooth, other than when you start hitting the system performance/graphics ceiling (which requires a lot)

6) Do you have desktop effects enabled?
 - yes, kde w/ lots of rediculous eye candy going on; widgets, monitoring, background changes, multiple windows VM's, RDP sessions, etc... 

7) Have you tried 3D / GLX? Does it perform well?
 - GLX running, but hasn't touched 3D. not many performance problems w/ GL, but what you normally run across w/ closed driver, and linux gaming in general

8) Can you stretch out a movie across all screens?
 - with 'EYEFINITY Desktop Configuration', yes(think 1 Giant X window); KDE, however, treats as individual screens, but window dragging across allowed

9) What kind of connectors do you use? DVI? HDMI? DP?
 - MDP - DVI active adapters (on every port: $26 on newegg)

10) Anything else I should know?
 - best to order your physical outputs, as you'd order your screens (left to right, etc...).  MDP0, screen 0 (left); MDP1, screen1 (center) , etc....  makes management, config easier in the end.
 - eyefinity support seems to be getting better on linux. check phoronix.com for specific reviews.
 - though this his is only 3 monitors out of 6 available ports, expansion across doesn't play as much of a factor as one would think, when it comes to the config. as long as physical lay out makes sense 

hope this helps