Do a search on google and you will get 21000 different answers on this question. I recently became an authorized user on somebodys acct. When I ran my FICO it bumped me up about 70 points (ran on MyFico.com). Yet some people online reference a 2009 law passed where authorized users can be "excluded" from being included in your credit report. Yet, I found yet another site where people mentioned that the 08 version of Fico does indeed included authorized users. I can list you a dozen websites from various reputable places, everywhere from CNN Money to Credit Card blogs. Half of those websites will claim it helps you. Half will say it absolutely will not. I'm dumbfounded.
I have no idea if having an authorized user on my account will help me with a lender pull. I just know that it bumped my Fico way up here and at USAA credit monitoring. We shall see if 6 months from now if I will be approved for a credit card. Right now, nobody will approve me for anything, even though my Equifax is pretty much clean. Will 6 months of an AU plus my secured cards help me? I have no idea. I wish I knew for sure but everyone online posts conflicting information.
After the big issue where stay at home spouses could not have the benefits of being an AU, they allowed the AU status to be factored in again.
My personal experience, I was added to by father-in-laws Bass Pro CC through Bank of America on Sept 3rd,2012, and as of Sept 26th it had reported to all 3 credit agenices. It bumped me from 602 up to 651 on my EQ through myFico, which matched exactly my lender pull. Now pre-approved for my first mortgage loan! 