There is a slight learning curve with using the mouse. You have to make a concerted effort to have good arm posture, rather than slouching your hand on the mouse like you probably do now. Once you are used to how the mouse operates, you can take better advantage of what it offers, and it feels much more comfortable.
I was surprised to find that there is almost zero resistance when rotating the mouse on its platform. This means that the mouse doesn't offer very much support when attempting to hold your wrist in an intermediate posture--your hand just falls to the extreme of the mouse's range of motion. The conscious discipline required to keep your wrist at the proper elevation makes the mouse feel kind of redundant: if I'm going to hold my arm up, why does the mouse have to move under it in the first place?
The 800dpi sensor on the mouse is plenty accurate for the average user. Obviously, this mouse is not for gaming: there are just two primary buttons, and the dynamic nature of the mouse's construction implies inaccuracy when aiming.
Tilt scrolling is unfortunately not a plug-and-play feature on Windows, though the immediate and personal email response I received from customer support said it works natively on MacOS. To activate tilt scrolling on Windows (XP, Vista, 7), you have to install their cheesy driver. The driver installs to your system tray, and doesn't allow options for removal. Also, the software offers DPI modes up to 1600, which is curious because the sensor is only capable of 800dpi.
Finally, the mouse is advertised as good for traveling, but its moving parts make it inherently fragile. I would not want to put this mouse in my computer bag unprotected or risk damaging its feet on foreign surfaces, for example. Some kind of a protective bag would have been welcome to aid travel.
In all, I felt that the ErgoMotion mouse is a unique and exceptionally creative concept for a device, but its execution is not quite perfected. For this mouse to be really comfortable, it needs to have a larger range of motion: even if vertical mice aren't the true ergonomic answer, they are still really comfortable and offer a position that's impossible with the ErgoMotion Mouse. Also, the mouse needs to offer some resistance in its motion to support your arm in more intermediate positions.
At an MSRP of $50 USD, the ErgoMotion mouse fits in nicely with other ergonomic mice on the market. Despite the flaws outlined above, the mouse is still comfortable and easy to use. For its innovative design and good comfort, the Smartfish ErgoMotion Mouse receives the OCIA.net Silver Seal of Approval. I look forward to seeing a second revision of this mouse in the near future.