Just updated my itunes and my library was wiped out. How do I recover this. Freaking annoying!

It has always been very basic to always maintain abackup copy of your computer. Use your backup copy to put everything back.

What's done is done; if it's wiped out now, it's too late to make a backup. But it may not be that bad. Are the actual files missing, if you look for them in Finder? (they would most likely be in an iTunes folder within the Music folder.)