Being as I've recently switched back to the Mac side on my work-issued Macbook just for the hell of it, I thought it might be interesting to keep a running list of pros and cons.
Disclaimer: still using 10.5.8. As all I do on this thing is surf the net anyway, upgrading is not a huge concern, but I suppose I'll go ahead and do it if the chance arises and doesn't cost me anything.
Also, some of my complaints are bound to be the fault of third parties in whole or in part, but since Windows often takes crap for this as well, I think it's only fair that my observations are not limited to things that are entirely Apple's fault (especially as I don't use very many Apple programs).
-longer battery life - this fairly well known, and while I still blame bootcamp engineering/drivers for the poorer battery life in Windows, it is what it is. If I had to guess, I'd say battery life in OSX is around ~15-20% better for my typical workload.
-the apple/command key - a lot of shortcuts/keycombos seem to be based around this one key, which makes being a keyboard geek a bit more intuitive than the ctrl/alt/shift/win clusterfreak you often have with Windows apps.
-command-tab - the way that command-tabbing keeps all app children under a single icon and brings them all to the front is nice.
-the apple/command key - not all apps are consistent about this. Firefox is the primary culprit for me so far. command-w closes a tab (just like ctrl-w in windows), and command left/right navigates forward and back (just like alt left/right in windows) but cycling tabs, which you would expect to follow the trend and be command-tab is actually ctrl-tab. I get that this is because command-tab already does something similar to alt-tabbing in windows, but it's still annoying.
-the dock - it's entirely a matter of personal perference, but I just don't find the dock to be all that whizbang great. It's not terrible by any means, but after using the Windows 7 taskbar it feels lacking in a few (admittedly esoteric) areas:
1)I'm used to launching my most commonly used apps with command-# (what would be the windows key on a PC). Every app pinned to the Win7 taskbar automatically gets a shortcut like this based on it's position on the taskbar. So for example I generally launch Firefox with command-1, Pidgin with command-2, etc. As you can also switch between apps and active windows this way, I have almost entirely stopped using alt-tab in Windows. The way command-tabbing works in Mac OS somewhat makes up for this.
2) bad and worse: wasted vertical space or autohide? - I'm currently going with the autohide option since "always visible" wastes a tremendous amount of vertical viewing space which on top of the ever-present top menu bar and the additional titlebar/menus of most apps becomes pretty egregious. Sure I could shrink the dock to tiny size, but it seems kind of clumsy to use like that, and is still fairly ugly with bits of desktop peeking through in both corners. Not to mention the combined height of even the smallest dock and the top menu bar are probably wasting more space than 7's taskbar, even on huge-mode.
-No snapping features (that I can tell) - this may be something that has been added in later versions of OSX, but anyone who has seen a Windows 7 commercial or used Windows 7 is probably familiar with the ability to "snap" windows to one side or another and fill exactly half the screen. This is great on widescreens and while it's not something I personally use often, it's sorely missed when I need it.
-keyboard web navigation - most common message boards obey the following principle: when i'm writing a post, I can hit tab once, then space or enter to submit my post. The same boards do NOT follow this convention in Mac OS. Hitting tab instead takes me to the location/address bar. In addition, binary prompts from websites on the windows side will allow you to confirm the default choice with either space or enter, whereas on the Mac side only Enter works.