I picked up 2 FTVS on saturday and rooted both without issue. Method is to use open dns to block the update sites and plug the FTV in with an ethernet cable before booting, itll fail and ask you if youde like to skip updating and just login in with your amazon account. From there you will be able to root and install recovery.
btw where did you pick them up from. The bestbuy and staples all have new stocks now. I'm looking for one more.