GameRager: IMO the fancy mice are for those who want a better feel(I'm used to cheapo mice...i'd rather not pay big bucks for a better grip) or more buttons(I like using the keyboard for most commands.).
Its not just for feel, they really do improve your game. They allow much finer adjustments then cheapo mice and are smoother when aiming at things. Also with really high dpi you can throw your sensitivty up really high so you can 180 within and inch or two of mouse movement and still make those precise shots at long range.
KavazovAngel: Best thing about Mamba (besides the DPI) is the ability to run the mouse in dual mode, wired or wireless (I think it can be changed on the fly, you just plug in the wire and it becomes wired).
Not a big fan of wireless, I would probably stick with wired regardless.
CalamityRanger: This was my only real complaint with it at first too. The mouse is technically rather gigantic so I have to drape my whole hand over it. :P You get pretty used to it though. Those side buttons I personally don't use in gaming, but I do find them rather nice to control web browsers' forward and back buttons. :)
Thats kind of what I'm worried about with the bigger mice. I keep my wrist on the mouse pad and move the mouse about in my hand without having to move my entire arm. Can you still do that with a deathadder?