I have a website that gets about 20 hits per day. I'm working on promoting the site, and am considering getting to the front page of digg, which could drive tens of thousands of visitors to my site in one day, and my server can't handle this. I'm wondering if I could move my site over to a dedicated server for a week or two and then move it back, as a solution to my situation. Is this a viable solution? Does anyone know of other ways to deal with this?
As Bohra said, cloud hosting would probably be the best bet. You can use a dedicated server for a couple weeks and move your site around, of course, but you're going to pay for a month of service. Not saying they don't exist, but I don't know any dedicated server company that lets you purchase less than a month of service.
I would suggest go for a small VPS and as you grow you can move around to bigger VPS or dedicated, dedicated servers cannot be rented for less than 1 month, in that case you will have to pay for whole 1 month and not only that, you are responsible for payment for dedicated server to renew it, so its really not a month before you need take decision, you need take decision in well in advance, and keep your site safe.
I would like to suggest cloud hosting too, let me tell you that migrating between hosting to hosting like shared -> dedicated and then after 2 weeks dedicated -> shared again is doing much more harm than you think it will, as it is very possible that your site will be down when migrating and the dns will propagated slowly at some countries/ISP, not yet mentioning the efforts for migration. My 2 cents..
I agree that some type of cloud or CDN solution would likely work best. Most hosting providers will not be interested in providing a dedicated server for you for such a short period of time though, unless they have an older, spare machine laying around somewhere. But they are certainly not going to offer you a new CPU for 2 weeks.