I did free US shipping over the Black Friday/Cyber Monday weekend last year, and got quite a few sales (for me). It was my first holiday season on Etsy, so I'm not sure how much had to do with Free Shipping and how much had to with so many people buying then. I didn't offer it the rest of the season and didn't make any more sales. I thought it would impact my profits more than it did. This year, I'm considering doing free shipping for longer, but I'm also doing four craft shows and so need to be mindful of my inventory. You can add it as a tag and put it in your banner, as well as advertise on Facebook, Twitter, etc.