How are they different?
On a hardware level: the Embedded Controller chip which stores the OSX encryption keys.
On a software level: the pretty GUI, covered in chrome
But seriously, I borrowed one (via VNC) the other day, and I'm starting to want a Mac.. and I'm a dyed-in-the-wool PC user (Linux, thankfully).
I did the very same thing a week ago.
Used my brothers mac for 30 mins enjoyed it and so wanted one I even started browsing the Apple site with a view to a purchase.
Then I skinned Ubuntu with Macbuntu, got the urge out of my system in 2 days, switched back to Ubuntu with gnome desktop and saved myself in the region of £1000!!!
Try it; and send me half of your savings