sometimes wireless wierdness can be associated with interference. Thats a really hard thing to test, especially since it looks like you have an iMac. If you had a portable I'd say take it to the park or somewhere that there would likely not be any interference.
If the problem persists I'd recommend getting a new mouse. The wireless Mighty Mouse by Apple is nice, but the style isn't my cup of tea. If you have the same feelings about the Mighty Mouse as I do then check out the
RadTech BT600 mouse (if your iMac has built in bluetooth. I'm really impressed with the mouse. It works well and has lots of sweet features.
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