They make it so you don't look friendless on your profile page.
OK, but more seriously, you may now privatize your profile. Currently, unregistered users may not see your profile, but now you may even customize that. One of the options is to only show parts of your profile to your 'friends'. Other than that, I can't think of what use they are..... unless you are into that myspace/facebook stuff and think it is cool to have tons of friends.
There is a whole bunch of new stuff in the FAQ including this -
Friends and Contacts
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