I LOVE my MS IntelliMouse optical... I have one at home and at work. When I stared my job I demanded one.
I've been using them for a few YEARS (about 5 now) I never had a ball mouse last more than a year or two MAX.
My favorite feature (other than never cleaning it and smooth tracking) is the back/forward buttons on the sides of the mouse. Most new mice with back/forward buttons do them both on one side of the mouse. This one has one on each side.
amazon is still selling them
http://www.amazon.com/exec/obidos/tg/detail/-/B00005TQ08/002-6464659-2423250?v=glance$23
I paid ~$50/ea for mine... and would do it again if I had to.
The reviews on amazon are pretty good. Sounds like it's even good for gaming.
The only downside to optical mice I know of is the surface. Don't even think about using one on glass. Or any reflective surface. Also if the surface isn't fairly smooth you can have problems. At work my mouse sits right on a seam of the desk which would mess up the tracking. True I could just use a mouse pad... But I just "patched" the seam with paper/tape. Works great. Although after a few years the paper/tape gets nasty.
--mizary