File types revisited
File typing has been a hot topic in Mac OS X ever since file name extensions became mandatory in Apple's interface guidelines in 2001. Philosophical issues aside, there are real, practical problems with file name extensions as a means to store and identify file type information. Let's even ignore storage issue entirely and focus just on identifying a file's type.
The first problem with file name extensions as a means to identify a file's type is that they are not unique. File name extensions are used on many operating systems, and there is no universal arbiter for which extensions indicate which file types.