Well, after about a year I started experiencing the "scroll ball problem".
After reading the posts, here's what I found useful - 99.7% isopropyl alcohol (in my case a "Klean-Kloth" thermal printhead cleaning cloth" and a can of compressed air (like the ones you get at the office store). I wiped the scroll ball with the cloth (with lots of pressure), after a few seconds, peices of crud started to come up to the surface. Squirted some compressed air to blow them away, and kept going with the cloth. Lots of crud came up, hair and fluff etc. I just kept repeating for about five minutes till nothing else came up. Then gave it one good blast of air to dry up any remaining alcohol. The mouse is back to 100% :-)

Would not scroll down. I tried it all: upside down & rubbing, compressed air, toothbrush, alcohol. Something worked, I'm not sure what, but I think as much as anything was putting the mouse upside down on the table and rubbing hard. I hadn't thought to abuse the thing like this but this thread enabled me.
Thanks to all for your help. I love my Mac and, well, the people who use Macs are cool, too!