Originally Posted by richalex2010 (Post 812407)

Not the case. Apple uses the HFS+ file system, while Linux uses EXT3. Linux programs do not necessarily work on Mac, as there are major differences due to the different heritages of the operating systems. OS X is based on NeXTSTEP, which is a Unix/BSD-derived system (using the Mach kernel). Linux is an independently, openly-developed Unix-like system. Linux is Unix-like, OS X is Unix-derived, meaning that they are not inherently compatible.
EDIT: Also, the biggest difference to end users with Linux/Mac is the UI; OS X uses the proprietary interface that Apple developed, while Linux uses one of many desktop managers, including GNOME, KDE, and XFCE to name the three most popular (to my knowledge).