(I like how the monitor is calibrated to perfection out of the box in Mac OS X. It didn't take too long for me to do the same in Windows 7 given it's easy-to-use calibration tools. (I find Mac OS X's basic mode to be insufficient, and advanced too cumbersome.))
Actually, on Windows, hardware acceleration also means that you get to have better text rendering in some cases Not to mention that I've had enough of Chrome stuttering while I'm scrolling fast. It looks disorienting when I see it. (There's a reason why I stopped using Chrome for the most part...)
It's probably one of these things that you won't notice, though.
Also, I wonder how does one attempt a middle-click on a Magic Mouse. (Didn't bring any mice)
I'm not, I use both Windows and Mac almost equally (on different computers, mind you). Though I've had my Macbook Pro for about 2 years.
Performance for 90% the time will be the same, however 3D graphics-intensive things (ie. 3D games) will usually be better (to varying degrees) on the Windows side, due to the better graphics drivers and the ability for games to run in DIrectX. Mac doesn't have DirectX, so games are often ported to OpenGL/CL which comes with performance overheads.
Browsing should be the same, provided you use a cross-platform browser, like Chrome, Opera or Firefox. That said, Firefox for Windows has hardware acceleration, so complex pages should scroll smoother.
The Macbook Trackpad in OSX is hands down the best trackpad on the planet. No competition. Under Windows, it's not quite as good.
Do you mean you already have data on there? In which case you could delete it or just deal with it. There's not much difference, to be honest, apart from much faster graphics on the new one.
By all means, you might need Windows for some things (yes, games. Although all of Valve's Source games run on Mac, if you're interested in those) - I'm not being a Mac zealot at all, I just hate it when people get a mac and only use Windows. They would be better off just getting a Windows system in the first place.
If I had to get another laptop and money wasn't an issue, I'd waiting for them to release a 13" Retina Macbook Pro. That said, I'm thinking that by the end of the year, I might get two SSDs for my Macbook and RAID them.