After using with the single-button mouse for a almost a month, I've switched to the Microsoft Wireless IntelliMouse Explorer. I've concluded that the single-button mouse is obsolete, and it is just arrogance and stubbornness that cause Apple to stick with it.
I've used the Microsoft mice on Windows machines for a while. Logitech and Kensington have some acceptable models, but the various Microsoft mouse products always feel best in my hand.
I initially looked at the Microsoft Bluetooth mouse, but it was $80 and it wasn't clear whether it would work with my iMac's built-in Bluetooth transceiver. I found the Wireless IntelliMouse Explorer marked down to $30, so I snapped it up.
I have immediately noticed a difference in how easy the Mac is to use. This is not simply a matter of familiarity with a two-button mouse. With the new Macs' large screens and increasingly complex user interfaces, selecting menu items from the pull-down menu at the top of the screen or Control-clicking something is much more cumbersome than simply right-clicking something. Similarly, it is much easier to scroll with a wheel than it is to move the mouse all the way over to the scroll arrows.
The IntelliMouse control panel allows a wider range of mouse tracking speeds. I find Apple's mouse to be too slow, even at the highest setting. Neither Microsoft nor Apple provides good acceleration behavior, allowing fine control when the mouse is moving slowly but also allowing quick movements across the screen. This was once a feature that made the Mac more usable than Windows, but Apple forgot to include it in Mac OS X.
Apple once had the best mouse for any platform. This is no longer true. My Christmas wish is that Apple will develop a two-button scroll-wheel Bluetooth mouse. Until that happens, Microsoft will keep yet another foothold on my Mac.