Construction + Ports
With the exception of the screen, black screen bezel, and a couple other minor pieces, the iMac is basically full aluminum. This makes for a more rigid, solid, and sturdy design vs. traditional "plastic" computers and computer monitors. Now, don't be mistaken. Many people overestimate the strength of aluminum. Apple does make the claim that they use aluminum in their computers to give them a stronger build, which is true. However, if you were to drop one of the aluminum MacBooks on the ground, from any height beyond a couple of feet, it most certainly will dent, bend, etc... The same thing goes for the iMac. If this thing falls of your desk, it's probably not going to walk away without damage.
Even so, all aluminum build does add to the strength of the new iMacs. More importantly is the look that all aluminum brings to the iMac. Previous versions of the iMacs had a black plastic back (rear screen). The new iMacs have an aluminum back, which gives a sleeker, more refined look in my opinion. The back of the new iMacs seem to wrap around the computer.
On the back panel of the new iMacs, you will find a Mini DisplayPort, a FireWire 800 port, four USB 2.0 ports, audio in/out ports, and ethernet. The power plug also connects to the back of the new iMacs.