I'd put a big Welcome Oprah Viewers banner at the top of it with a sales pitch leveraging that social proof for all you are worth and giving them "special" advi

I'd put a big Welcome Oprah Viewers banner at the top of it with a sales pitch leveraging that social proof for all you are worth and giving them "special" advice for using the site, by the way. ^^ This. You are in a unique position of being able to PLAN for a huge spike in traffic. While planning for the technology impacts are important, do NOT forget the business aspects. You already have a damn good idea of the demographics of more than 100k visitors that might be visiting that day, so get started now. Do you want to offer a special "discount" for Oprah visitors that day? Does the signup process need to be simplified for less tech-savvy visitors? I definitely agree with Patrick that you want to have a targeted set of instructions or otherwise customized copy for the visitors that will come that day. Above all else, PLAY UP THE OPRAH CONNECTION! A banner, special icon, her picture, etc. Visitors should be smacked in the face early with some indication that they have found the site mentioned on Oprah. You might also want to find any Oprah-related message boards and create accounts now. Then on the day the site is mentioned in Oprah, go to those message boards and post a clickable link. Not only will this help the visitors get to the correct site, but they can use it to share the correct link with OTHERS.