Since Maya first came out, I'd been using a 3-button mouse with no wheel. I thought it was the only way to go. My last job was working on games at Microsoft. Everyone there uses a laser mouse with a wheel. It was a little awkward at first, as I expected, but I got used to it after a couple days and haven't noticed since. In fact, I bought one for my own computer to replace the 3-button one that I used to swear by.
The problem I see with setting the right button as zoom is that the right button has it's own function that's used ALL THE TIME. Situation-sensitive menu.