Well is funny. I just cleaned my BT Mighty Mouse with a damp cloth (no batteries inside etc), let it dry out and now the ball has gone really stiff. It takes a lot of effort to actually scroll. The sound of my finger pushing across it is now louder than the ball "clicks" too 
Any help on this? It feels like it might go itself after a while. But I'm not sure. And with my Warranty still in place I might have to get a new one. This isn't right at all! It's so bad that attempting to use the ball results in the middle mouse button being pressed!
Any help on this? It feels like it might go itself after a while. But I'm not sure. And with my Warranty still in place I might have to get a new one. This isn't right at all! It's so bad that attempting to use the ball results in the middle mouse button being pressed!