A modern iMac is painful to use. Your choice: place every app in the upper-left corner of the screen, or move the mouse over a thousand pixels each way.
Don't ignore Fitts' Law-- the menu bar at the top of the screen has an effectively infinite height, so even though you have to move your mouse farther, you can just slam it to the top of the screen and only have to aim horizontally. This is actually more important with higher-resolution screens, as the UI elements are smaller (at least until we finally get a resolution-independent UI, any decade now...).
Besides, the idea is to use keyboard shortcuts for menu items you use frequently. Much better than having to aim for a tiny rectangle on the screen, wherever it's located.
The OSX dock is unusable too. The fact that an app is running is indicated by a tiny dot under the icon.
For better or worse, Apple is trying to do away with making users know or care about whether an app is running, much like how things work on iOS. For example, there's a new API in Lion called Automatic Termination that allows apps to let the system automatically terminate them when the system needs to free up resources. See John Siracusa's Lion review for more details.
The fact that a second instance is running (rather difficult to do BTW) is indicated by a second icon located nowhere near the normal dock icon. You don't get a second dot. Seriously, WTF?
Oh, come on. How common do you think it is for users to want a second instance of an application, rather than just another window? I mean, I've only wanted to do it maybe once or twice in the five or so years I've had this Mac, and I'm very much a power user.