- Overall, developer reference documentation on Apple's Developer site seems more current and easy to understand than that on MSDN. A nice touch is the reference to examples which use a particular method inline with the documentation of the method <example> (MSDN does it using inline code, so it's not too different). My favorite feature about documentation though is the logical grouping of methods and properties arranged by tasks - that makes it very easy to get stuff done. I think this is the result of being the underdog in this space.
- Mac OS X applications' uniform usability and consistent aesthetic isn't a fluke. Apple's documentation regarding recommended usage is precise down to individual visual controls and yet comprehensive as far as Human Interface Guidelines go.
- XCode doesn't have anything on Visual Studio. Visual Studio seems, hands down, a better integrated development environment and debugging application. VS 2008 is really pretty awesome.
- Cocoa is nice, but still has some catching up to do with .NET. Cocoa libraries provide just enough abstractions to get stuff done, but they don't seem to be nearly as comprehensive and well thought out as the .NET libraries are. I found myself cursing some abstractions/APIs in Cocoa for their primitiveness compared to Windows pretty often. Generics give .NET an edge that Cocoa still doesn't have. Microsoft has done a great job of handling little things, such as boxing, which make development easier than it is for Cocoa.
- XCode and Interface Builder are unfortunate crutches required for Mac OS X development - I would claim that it's impossible to write any decent application without using both. This sounds great until you realize that IB, which really is a designer, does so much magic for you that you just cannot with code. Linking up IBOutlets, for instance, is something I cannot imagine can be done outside of Interface Builder and has way too much magic associated with it. As a developer I often felt at the mercy of these tools, instead of being the master of it. It's fortunate that this is not true of developing for Windows - there is a lot of helpful magic that Visual Studio builds in but it's certainly not required to develop a decent application.
- Overall, the Mac platform (Cocoa) seems more closed than it should be. This sounds weird, considering that it's all basically Unix and standard Unix libraries are provided or can be added relatively easily. My comment here related to how accessible and complete Cocoa/Carbon libraries are. Getting access to weird parts of the system is easier on Windows that on the Mac platform, I believe.
- Deploying Mac applications is a snap, better than Windows. However, I think this is related to how developers are accustomed to (ab)using resources in Windows (registry, etc). Not having a lot of Windows' 'legacy' facilities on the Mac makes developers think hard about what their app really should be doing. I claim that good developers should be able to create x-copy deployable apps even for Windows, though, so it's unfair to blame the platform here.
- The fact that it's built on Unix makes the mac support a lot more languages, especially scripting languages, out of the box. Windows is catching up fast though - integration of interpreted languages with .NET and PowerShell bring it at par with the Mac (I hear it might be better, but I don't have much experience).
- Testing on the Mac seems easier. The fact that there are a very finite set of configurations compared to the Windows platform makes life less complicated for developers. It's almost true that if it works on your Mac it's probably doing to work on most Macs (modulo a few exceptions). History says this has traditionally been an advantage of the Windows platform, but I'm not so sure it's a good thing anymore. This one's probably the most controversial of my observations above and likely to change as I do more Mac work.
So, who wins? I would say Windows for the overall developer friendliness. Apple has some catching up to do in several areas. That said, the Windows platform could learn more than just a few things from what Apple seems to be doing right.
It's a fun time to be a software developer.