Why is my Mac "falling asleep" when it's told not to? MY power settings are for "NEVER" when it comes to sleeping with AC power. AC power is always on. So why always when I come to the Mac after hours of being away, it awakes from sleep, loads up all the programs, signs back into skype etc. Where is the hidden setting that causes it to do that?

It only does it at home, another MBP I have at work doesn't exhibit this strange behavior.
Is your computer actually sleeping, or is it a display sleep that looks like a real sleep?

What about the other options in Energy Saver, like "Put hard disk to sleep when possible" (unchecking this may help with being logged out of some chat programs) and "Wake for network access" (checking this helps with other chat programs)?

Also check the schedule button to make sure no sleep schedule got accidentally set.

In my experience, all of the sleep options are controlled from the Energy Saver panel, so I'd check your system preferences first.  If that doesn't do it, check the settings in any third-party system extensions you have that might deal with power or computer performance.