Well well after some thoughts and re-reading this thread over and over. Applied some general rules that we outlined a bit through the discussion...
Here is what i used to have:
http://i67.photobucket.com/albums/h312/medski/Ui_8.jpg
And here's the work in progress:
http://i67.photobucket.com/albums/h3...i/IolUInow.jpg
I know i broke the no pic rule :p But a pic is worth a thousand words.
Since i raided with the second UI, I must say, the Unit frames under the character and in center of screen helps a ton. It feels like i really do know a lot more of "what's going on" than when it was in top left. The raid panels takes so much less space i can now see my surroundings a lot more while still viewing my raid. Added "Clique" to map De-poison, de-desease to mouse buttons and adjusted the fade range of the frames to 30 yards. That way i see who i can decurse and do so with just a right click or mid click. And i dont need additionnal windows to monitors those decursing things.
The combat log moved under the chat like in default UI, Tweaked SCT to have dmg on me on right, heals on me or that i do on left, special event in top center (of my character).
Slimmed down the FuBar addons to what i was using the most the rest sits away of immediate visibillity.
Overall feeling: I see more things, i can react faster to what needs to be done. I am in general more aware of what's happenning to the whole raid at any given time because all the info is displayed in a centralized manner either in my raid frames (or party frames in 5-mans, wich is hidden but at the same place) or unitframes, target and ToT. and battle events are around my character. I dont need to take my eyes off my character (or if i do its very short and close to my character) to see anything i need to see.
This thread helped me tons in terms of design and optimization of my UI, as well as reminding me how to tell what is it that i /need/ vs what is just fluff.
Thanks :)