Beside scrolling I often use 2finger flick right/left for back/next in safari. But with BetterTouchTool you can customize and add pretty much everything.
Yes it does. Though after playing around I switched back to the standard gestures. The only thing I used was 3 finger down/up = page down/page up for faster browsing boards. But after the scrolling update I don't need that anymore.
Also, can the mighty mouse work on more than one mac?
Yep, but you need to disconnect it in OS X. You can't use it on multiple devices at the same time. Wouldn't make much sense though.
BTW: if you didn't know: you can connect the magic mouse with just a long click. Very handy (didn't know that first and always connected it via Bluetooth settings in OS X)