1. The dock is cool, the Windows 7 Task Bar is cooler - specifically, if I want to minimize a window, I click on the task bar and it minimizes. Maximize it? Click on the task bar. Pretty cool stuff there.
2. Themes and Customization - Come on Apple, when OS X debuted ten years ago you promised us the ability to customize the look of the OS to meet our needs/aesthetics. Where is it?
3. Menu items - Why have menu items listed at the top of the screen ALL THE TIME? The integration of Menu Items into individual windows frees up screen real estate.
4. Censorship - As far as I know, Microsoft isn't censoring anybody on their products. Stop that, Apple. It's bad form. Now I can't buy overtly sexual apps in your app store but I can rent and download 9 1/2 Weeks or Original Sin? Ummmmm, what? Take all the apps you don't feel are "necessary" and put them in a completely different genre in the store if you want, but don't boot them because you feel they're not necessary to the user. Are people using them? THEY'RE USEFUL!
Now a list of things Microsoft could learn from Apple:
1. Networking isn't hard, don't make it needlessly difficult just so your certified pros can hold onto jobs.
2. Develop your own hardware to sell you OS on and control the quality of it - I'm not saying try to put other computer makers out of business, but learn from Apple's total oversight of the hardware they produce - even if you don't like their OS, the hardware they put out there is always ranked exceedingly high in quality standards.
3. Quality Control - Seriously, Vista should never have been released as it was. Stop the "Release it now, fix it later" doctrine and get it right the first time. With any luck, Windows 7 is a glimpse into a brighter future in regards to that.
4. Stop trying to play catch-up with technology you didn't come up with. The Zune should be put out of its misery and let go. Focus your attentions on your strengths and build out from there. The upcoming Courier from you guys is unique, useful and and appears to offer much more usability than the iPad right out of the box.
I could easily go on for some time on both lists, but I don't want to rant too much.
I honestly feel if you put the best aspects of both into a single OS, it would become the one OS to rule them all!