I believe one would be really enlightened and suprised at the behavior and viability of yeast under a microscope. I have never examined yeast under a scope but sure would like to give it a try sometime. My wish list is pretty long and getting longer.
I have a microscope and counting chamber, and started the thread to get an idea if and how folks are using these. What I can say from my very limited experience is that the quality of the microscope is important. New student and lab microscopes are very expensive, costing hundreds if not thousands of dollars. Toy microscopes will not give you a quality approaching that of a 100 year old lab microscope. They have plastic optics, and really don't work well. I found a high quality (Leitz) microscope from around 1950 on craigslist for $100, and have been very pleased with it. If you can find a decent quality lab microscope it will be of a far greater value than a new, inexpensive, microscope.
I have followed the procedures Kai linked to, which are similar to those on the Brewing Techniques site and elsewhere, and the cells are easy to see and count. I have not worked on the staining yet, but will note that you can also find Meth blue in the pet supplies for aquarium use, its inexpensive, and would work well. The yeast does not really "behave"... it just sits there, and using a 40-50x objective they just look like little spheres in the counting squares. The math is tougher than the microscope.