The on the fly DPI is a gimmick and is more of an annoyance than anything give me the full 1600dpi not 400/800 that I can get from a cheap mouse.
I also love that when you flick the mouse really hard - but don't move it very far - the cursor moves really far, I can do 540 with one flick where it would take will the whole mouse pad to do it slowly.
i have the diamondback plasma. i personally think its not that comftorble. buttons are kinda big and are easily pressed. the right two buttons are pretty useless since you can't easily use them with ur right hand. or if ur left handed you can't use the left side buttons. i rather got a logitech since the mouse is more comftorble.
the best Logitech mice are the G5 (wired) and G7 (wireless)
I have a G5 personally
on the G5, the buttons next to the sctroll wheel are to adjust sensitivity.
on the MX-500, MX-510 and MX-518, they're to scroll up and down, and also to change the active window (I also have an MX-510)
Why? I love it, it means that I don't have to change the sensitivity when going from a sniper to a normal gun and I can do random spin on the spots to scan the area.