I agree with grellas that while Digg or Reddit (really their legal counsel) could technically claim a copyright in the legal written work that you are adapting for your own use, realistically suing you for copyright infringement on their terms of use and privacy policies wouldn't be worth their time, and you could potentially assert a successful defense of fair use. I don't know the specifics of your business so I can't give you specifically tailored indemnity, privacy and use of information clauses for free (yet!) but that type of work is not hard for a lawyer, really shouldn't cost you very much and shouldn't take long (a couple hours). The much bigger issue in my opinion (and why copying Digg, etc long term isn't a good idea) is whether adapting their policies will adequately protect your rights and liabilities and those of your business well, especially those idiosyncratic to your business. If you just need boilerplate for the time being you can avoid this whole issue by using privacy policy and terms of use generators; I found a few here:
http://www.bennadel.com/coldfusion/privacy-policy-generator....