Jeremy from ArsTechnica has an interesting review posted of AmigaOS 4. He covers everything from the installation to productivity and multitasking, and came to some surprising conclusions.
"Because the OS and its applications take up so few resources, it is possible to run an entire suite of programs - my typical usage is ten or so pages up in a browser, an IRC client, an MSN client, a text editor, a command shell, a 2D graphics editor, an e-mail client, a word processor, and a media player - and still have all these elements fit in a mere 256MB of RAM. Because the system never pages out to disk, switching between these applications is instantaneous: I cannot physically hit the Amiga-M switching keys faster than the OS can respond. This is a marvellously enjoyable way to work: you are never waiting on the hard drive or the operating system when you switch from one task to another."
Now, all we need is some hardware to run the thing on. Personally, I'd love to setup an AmigaOS box alongside my Windows PC.