We weren't talking about it until a Windows user bought it up in a Mac forum.
Individual files - mostly plist files and sqlite databases.
No. The program files are contained in one place. Your configuration files for each app is stored in two places. /Library/ somewhere for system-wide, and /Users/yourname/Library/ for user config. If you just drag and drop something from the /Applications folder to another machine, you basically get a fresh install.
There are exceptions to the everything-in-one-place way. Some applications vendors still have Windows mentality and just install their **** all over the place. Microsoft, for example. Office dumps a load of stuff under ~/Documents instead of ~/Library - I really hope this is fixed in the new version.
Some other applications, I imagine VMware/Parallels/VirtualBox need to install stuff at a system level to work at all. I seriously doubt they'll just work if you drag/drop them to another machine. But usually they're pretty good about setting themselves up the first time you run them, so it should be reasonably straight-forward.