How is "craft()->fileCache" different from using cookies? Just looking for a little clarification on the craft()-&gt;fileCache method...

Everybody already knows that when a cookie is set, that cookie only exists on the end-user's computer. No one else using the website can access that cookie.

But if I were to replace that cookie getter/setter with the craft()-&gt;fileCache getter/setter methods, is that data now available to everyone? Where a cookie is stored on the client machine, the fileCache data is stored on the server?

This is what I suspect is happening, just trying to be sure that I'm interpreting this correctly.
Correct... craft()-&gt;fileCache will save to your craft/storage/runtime/cache folder by default, which will have a .bin file that has a hash of the key you provided when calling set() and the contents will be a serialized version of the value you passed in.

Also worth noting that while craft()-&gt;fileCache still exists, as of Craft 2.0, it is simply a shortcut to craft()-&gt;cache, when the cacheMethod config setting is set to file.