Pretty Much Windows Side Only
I'm a PC user so I'm basically planning to use Windows 7 exclusively on my Macbook Pro. I only left about 13GB free on the Mac side because I don't see myself using it much. I also bought a Macbook for my brother last Christmas and he never uses the Mac OS. I'm not sure if he even remembers how you boot into OS X and he probably wouldn't know how to use it anyway. I partitioned his drive with about 80% of it allocated to Windows because I doubted he would ever want to learn to use the Mac, but now I'm wishing I had allocated more to Windows.
This is my first Macbook so I've been switching back and forth between OS X and Windows 7 just to learn how things work on the Mac side and see if something would entice me to switch. Both operating systems work great and have their pluses and minuses, but I think I like Windows 7 a lot more for a variety of reasons.
Visually speaking Windows 7 & Aero are a lot more colorful and pretty with great transparencies and taskbar window previews. There are a lot of things in OS X that I find annoying like the dock/taskbar which in my opinion just wastes the screen's valuable vertical real estate and does a poor job of showing you which windows are open. If firefox opens up multiple windows I have to right click on the taskbar icon just to see how many instances are open and to switch between windows. You should be able to just glance at the taskbar and tell how many windows are open without having to click or press anything. In OS X if you want to resize a window you can only do so by grabbing the lower right hand corner. I also had a tough time getting some applications to maximize and fill up the whole screen exactly the way that I wanted. In windows you can grab any part of the window or just slide it to the top or sides to resize exactly how you want. And the menu bars in OS X not being attached to the windows is just something that is really irritating especially if like me you use multiple monitors. And it would be very annoying when I'd hit the close button on an open application only to later realize the only way to actually shutdown the application completely was to go into the menu and select quit. I guess the overarching problem with OS X is that I found that often times windows and programs were open that I did not desire to have open. I have the same problem with Windows Mobile which seems to not want to let you easily shutdown anything. I also had a slightly buggy experience running my external monitor with frequent flickering using the mini display port adapter. When I use the same monitor in Windows I get no such flickering, probably because OS X is doing some power management on the GPU. On the subject of external monitors I found it really disappointing that there was no option available to select only displaying on the external monitor like there is in Windows. There is a way to trick the macbook into shutting off it's screen but it is much more difficult than should be necessary.
On the plus side of OS X I like the way that it handles finder/explorer menus. It is much cleaner and faster to move between and make changes in OS X settings. Control Panel in Windows has gotten ridiculously overcrowded and is too complicated to navigate. In terms of settings I found configuring network settings and setting up networked printers much easier and more straightforward in OS X than in Windows. OS X widgets are a million times better than the lame Windows Gadgets and might be reason enough for me to consider switching if not for the fact that Yahoo Widgets makes both alternatives irrelevant. OS X screen savers were also better, but I don't use screen savers much anymore. I liked the ability to slide all open windows out with a button press or 4 finger slide with Expose. The multi-touch navigation in OS X is very nice and I'd love to see it incorporated into bootcamp. That being said Windows 7 handles the open window browsing pretty elegantly with the new desktop preview button in the taskbar, the grouping and preview windows in the new taskbar, and the "Windows + Tab" preview. The biggest reason I ever see myself going back to OS X is the better battery life and power management with features like ambient light sensing.
I don't use much software that is exclusive to Windows, but one program I use a lot is the Slingbox Player and it is infinitely better on Windows than it is on OS X. On Windows Slingplayer supports streaming at HD resolutions, it records up to an hour of streaming on the HDD, and it includes a great Zap2It tv guide menu. All these features are missing on the outdated Mac version. Another small problem I came across was playing back Windows media video. I was able to install a program that could import the video and play it back in Quicktime, but it was incredibly slow. I also tried Video LAN player but I had problems then getting the audio codecs to play. I'm sure if I really wanted to I could get all the video and audio files I have playing on OS X, but in Windows 7 I didn't have to install any codecs myself and every video and audio file I owned worked from the start. I only play games on consoles, so that is not a consideration for me.