>Noticed the wheel on the mouse was getting a little hard to move, so I popped open the mouse to clean it out. Yikes! Pulled out clump of gunk that was piled up around the wheel mechanism, then picked out the impacted stuff in the wheel itself using tweezers. End up with a rather sizable pile of gunk...

Gunk factors:

1. Woman who is a regular or heavy user of hand creams/moisturizers
2. Presence of long-haired cat or dog
3. Eating "al desko"

Any one factor is gross.
Any two factors creates a biohazard.
All 3 factors makes for a SuperFund site.

Another way a mouse can get gunked up: most glide on the mousing surface on 4 smooth Teflon or hard plastic pads. Over time these pick up gunk too, and make moving the mouse around more difficult. You can usually flick the bits off with a thumbnail but few people ever bother to do so.