It is definitely finger sensitive, a fact that is even promoted as a feature in the product information. Even if you get used to the need to not rest multiple fingers on the mouse, it still presents a problem for if you want to press more than one of the top three "buttons". That isn't something you can do right or wrong, it simply doesn't work.

To be completely correct about it, there are three physical buttons. The side buttons are the simplest as it is just squeezing. The left and right click functions are implemented using the same button by sensing where your finger is located. This fails if you rest your fingers on the mouse or want to use both buttons at the same time. Last is the wheel, which actually doesn't get clicked itself. Instead, when the wheel is pressed, the main button functions as a middle mouse button. All together, this means you can only have two of the four "buttons" pressed at any time.

I omitted the details for the sake of simplicity, as it is mainly the left vs right function that is problematic.

Unfortunately, I've found the Mighty Mouse completely unusable. They continued using a single button, and instead it senses where your finder is to determine if you are left or right clicking. If you rest your fingers on the mouse, it can't detect this properly and instead always registers a left click. I wasn't able to get used to this and instead just went back to using the trackpad.