I bought the steelseries recently and really like it. It is huge though compared to a standard mouse, I don't find it uncomfortable though (really weird using the standard size mouse at work now). I have two current issues that I haven't got around to solving:
1. If you have more than one wow open it will send button presses to both windows, won't be an issue if you only play one account.
2. Related mostly to healing. You can't mouse over unit frames and cast spells using the buttons, a lot of my healing macros use mouseover in them (so I hover my mouse over someones party frame and press 2 and it casts a heal on them) if I try doing this with a mouse button then it doesn't work.
I'm assuming both of the above problems could be solved by binding the mouse buttons to keyboard keys, but my keyboard already has extra buttons that I've had to bound like this so I'd prefer to keep my extra mouse buttons as actual extra buttons, not just more accessible buttons.