I think the "Wow" factor for me is just the amount of time I don't waste.
I spend a lot of time working on Windows and *nix machines, so I appreciate how little (read: virtually none) time I spend maintaining my personal machines.
I would also argue that developers working on the OS X platform have a better sense of "usability". Take for example Cyberduck. (
Cyberduck | FTP, SFTP, WebDAV & Amazon S3 Browser for Mac OS X. )
It took my roughly 30 seconds to set it up for a co-worker who is only computer savvy enough to do basic emails tasks. Yet he now uploads / downloads files via FTP on a daily basis.