I'm currently on my second Cataclysm mouse and shopping for a permanent replacement. I'm not the least bit excited about finding an alternative because despite its setbacks, I absolutely love using this mouse in game and I have no idea how I'm going to adjust to a mouse with fewer buttons. I play a tanking class in warcraft and the numerous buttons at my fingertips make it exceedingly easy to adapt to the gameplay during heroics and raids.
My issues so far:
First off, the presets for the mouse are stupid. I don't need a special hot key on my mouse to open my bags, check my guild, or bring up my charecter screen... I do those actions maybe once or twice a day and I have no issues with going to a menu for that. I personally want my 17 buttons to be all for combat and vent controls that I can easily bind with my Bartender UI. However changing the settings to do that was a pain, and my second issue.
The Steelseries UI won't let you just re-assign a mouse button to a letter, or a number. So if you want mouse button number 14 to actually be the letter "P", you have to scroll through a list of "Actions" until you find "Open Spellbook" (which in warcraft language equals the letter P). If you're using this for anything other than Warcraft, or maybe you don't know that there's a letter bind for checking your PVP currency, the process can get really annoying. However after I had that all figured out, and the mouse was now bound to letters that I could re-assign to combat bars... I fell in love with it.
Until lastly, issue three. For some unknown reason, my mouse loves to lose tracking and go into these 5-6 second seizures on my screen. The best way I can describe it is that it looks like the cursor is in a paint mixer and violently shaking up and down. I can get it to stop immediately by hitting the spacebar, or unplugging the mouse and plugging it back in... but the problem always comes back. In a dungeon or raid it becomes detrimental becuase I can't click on a mob, and if I'm looking around when it happens my view snaps all over the place. Worse is when it happens while I'm flying and guiding my mount with the mouse because I'll suddenly take off in 15 different directions while my buddies laugh at my toon. I've swapped out the mouse at Best Buy, re-installed the drivers, used different USB ports, and disabled its special features in-game, and I get the same results.
I'm still looking for a solution to the issue but in the meantime I'm also looking for a new mouse. I haven't seen anyone else with this problem so I'm assuming it's my computer, but since Computer Cost > Mouse Cost the mouse has to go.
So if you are using it for Warcraft, you can re-bind everything ok, your hands are somewhat large, and you don't get the bug... you'll really enjoy it. If not, then you will be looking for a replacement like me.
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Edit (5/23/2011): Eventually found the bug was caused by a conflict with software that was running in the background. My laptop had a program that would stop inputs from my touch pad when it detected a mouse, and I found that erasing this program and manually stopping the touch pad when I needed to was an easy fix. Still not sure why the Cataclysm Mouse was the only mouse with an issue, but that fixed it for me.
Sadly though, I've since purchased and trained myself to use the Razer Nagga MMORPG Mouse and I'm pretty happy with that. Setup was a breeze (the buttons are all pre-assigned to your number pad, so it was cake re-assigning those to action bars and macros in-game), and while it's intimidating as hell, having 12 buttons for your thumb to use eventually becomes second nature and easy to use.
Like I said above though, I loved the Cataclysm mouse and if I wasn't so used to another MMO mouse already I'd go back in a second.