First, a random note on the screenshots: I'm one of those quirky people who puts the app controller on the side of the screen. I wrote up why on my blog about 5 years ago: there are a few advantages, first and foremost is how it makes better use of the "widescreen" format laptops and monitors now sport (I mean, have you seen how short the screen is on a 11" MacBook Air?)
So to the left is the Windows taskbar and the right is the OSX dock... both have their graphical bells and whistles. Windows (at least as of 7) has some translucency going on - on my work machine it's really sophisticated, with an "active window" highlight color and some pretty light effects as the mouse passes over it. The Dock has that terrifically fun "magnify" effect, where the icons fluidly grow and shrink as you pass the mouse cursor over it.
The primary difference between these two bars is this: The Taskbar is Window based, the Dock is Application based. This is why I think the Windows approach is superior for a multitasking operating system: each window maps to a task, a bit of state I might want to return to, and the Taskbar offers a passive, unobtrusive reminder of each window and a way to get back to it. (Kind of a dynamic "todo list") With the Dock, each icon is an application. There is no direct jump to a given window, just that application. (OSX offers some other paradigms for getting back to where you were, more on that in a bit.)
Let's start with Windows. Every window gets its own place in the task bar... (before Windows 7, the "launch a new program" icons were either hidden behind the Start button, or later, on a little specialized "quick launch" piece of the taskbar. Nowadays you always have the option of "pinning" an application to the taskbar, which comingles the running and launching icons.) The difference between a Window of a running program and an icon to launch a new instance is obvious: the former is a button with a caption, the latter is just an icon. (
With the Dock, the visual difference between a running and launchable program is minimized: a small white dot. Click on the icon and its windows move to the front. Again, to me there's a huge difference between a running program (carrying state I want to be reminded of or get back to) and a launchable program (which is a clean slate) and so I find Windows' approach to be superior.
This App-centric approach carries through to the quick switching. With Windows, I hit alt-Tab and I see a sorted list of my windows. OSX has a similar function, but again I'm looking at placeholders for whole apps, not a window at a time, once I switch to the right app I still have to find the window I'm thinking of. I know there are different apps to adjust the OSX environment, but I think getting the defaults right is crucially important-- having to relearn how to get around a friend's computer running the same OS because they don't have the same "fix" installed stinks.
It could be argued that I'm doing it wrong, expecting OSX to act like Windows instead of adapting to what OSX offers. For a long while OSX has had exposé, a single button that temporarily resizes and repositions all of your windows (or makes snapshot thumbnails, based on how you think of it) so that they are all visible at once. OSX Lion's Mission Control furthers that paradigm. While I might be getting old and curmudgeonly, I don't like exposé as much as Windows' system, in part because it lacks the "quick bounce back" of alt-tab, where a quick tap of alt-tab brings me back to what I was last working on (Windows has a really good "most recently used" algorithm for tasks, an easy to miss but hugely important detail that Just Works.)
UPDATE: OSX does have cmd-` (very easy to find above cmd-tab, kudos for that choice) that cycles through open windows of the current application. But this interaction is application oriented, you can't gracefully leap back to what you were doing in a different application like you can with Window's alt-tab.
(I guess I should say, Windows 7's defaults are a bit different than what I'm describing here... I set Windows to "Never combine" Taskbar buttons, and so I don't see the roughly exposé like thumbnails Windows makes now.)
This differences harken back to one of the oldest differences between Windows and MacOS-- with Mac, there's one place on the whole screen where the "File" menus will appear: each app takes over that space. (It's kind of ironic that it took OSX so long to get fullscreen mode right.) This kind of points to the idea of Mac as "information appliance"-- the whole machine is dedicated to that app. On iOS I find this perfect and relaxing, but I find it irksome on a multitasking system. (I know people argue that there are advantages to the menubar-on-top paradigm of Mac, that you always know where to look, and your mouse can target the menu faster, but for me those bonuses are outweighed by having to figure out which menu bar applies to which window.)
I have some more thoughts on Windows vs OSX, but that can wait 'til next time...