Multitasking With iOS 4 is Horrible: Apple Blew It
pcworld.com
pcworld.com
However, the author points to the unruly tray and how you now have to close applications that you don't think you're actually running. This sounds very similar to OSX to me, where in the tray you've got programs you haven't used for weeks, but they don't close when you shut the window.
If apple 'blew it' with the tray, then I'd argue they blew it with the tray on OSX, which I do feel is more of a pain with all it's notifications, and icons for apps I'm not using anymore.