@Rory: Yeah, it never really got used like it was supposed to. On the other hand, exactly the same limitations are in place on the Windows Tray as in the OSX equivalent (only running programs), the only difference is in how it’s (ab)used by folks developing for Windows.
Not an issue for most users, though, who use the available tools to hide the icons they don’t want to see even if they’re not capable or unwilling to stop the program from running. In my case, I’ve got 3648 horizontal pixels, so I might let them go a little bit more wild than I would on a smaller desktop.
BTW: Quick Launch is dead since Windows 7’s “Dock by any other name), and the Start Menu has (at long last) been as-good-as replaced by something far more like Quicksilver. The System Tray and the Desktop are just about the last bastions for lazy developers to litter with icons, now (and boy, do they still litter them with icons if you’ll let them). Windows is getting there on user interface design, slowly.