I've just replaced the microswitches of my Logitech MouseMan Optical dual sensor mouse. I bought it about 6 years ago for about $80 and I was extremely satisfied with it until the switches broke.
Today I managed to get some Omron D2F-01 switches. The original switches are Omron D2FC-F-7N parts but they have been obsoleted. The new switches have a crisp tactile feel which I love, altough they are a little bit harder to press than the old ones.
Being able to replace the switches is one of the "secrets" that manufacturers don't want you to know because chances are you wouldn't have to buy any other mouse ever again. There are other temporary fixes to solve the issue, but replacing the switches with new ones is stongly advised.