Mac OS X defaults to hiding the users Library directory. No doubt, this was changed to keep novices from deleting necessary system files. Those that wish may show the ~/Library with the following command from Terminal.
chflags nohidden ~/Library/
If you wish to return to default settings you can hide the ~/Library with the following command.
chflags hidden ~/Library/
Note that the user Library is always available from the command line whether it is hidden or not.