It's not a "foreign OS" for the mouse since Microsoft makes an Intellimouse driver for OSX and the current version is 8.2 and it works with all versions of OSX right up to the current Mavericks here. That driver supports all the extra buttons, etc. along with application programming for the functions and even a mouse wheel accelerator option which is pretty spiffy for fine control at slow speeds and ramps up the acceleration if you spin it faster down a web page or whatever. The docs claim the newer wireless verisons, etc. all work as well. Personally, I like the "Intellimouse Optical" wired model. It just feels right. I ordered several when I found out they updated the mouse to a newer crappier design. I have one on my 2008 Macbook Pro and on my 2012 Mac Mini. It works fine on both here in Mavericks.
My extra button functions work immediately on boot. If the Microsoft driver was installed correctly, it SHOULD be showing "MicrosoftMouseHelper" in your user login settings in preferences (Users -> You -> Login Items). If it's not there, that's probably why the extra features are not starting at boot time.
The only problem I've had is that on the Mac Mini, the mouse sometimes/often freezes when waking from sleep until I unplug/plug it. The same mouse does not have this problem on the Macbook Pro with the same version of OSX, so I'm not sure what the cause is. Worst of all, it doesn't do it every time, so it's something strange. I have a LOT of USB devices plugged into the Mini (two 7-port hubs with a total of 12 devices plugged in), but it does it even with all those removed so it's probably something else in the wake cycle.
