The question often arises - "If I move my web site to a new host or a new server, will it affect my search engine rankings?" The short answer is no, as long as you do it right.
Clients move their web sites to a new host or a new server for a variety of reasons. In most cases, it's just a matter of moving your site files from one machine to another. So, if the domain and the site stays the same, then moving the site shouldn't cause any affect at all in your rankings. There are a couple things you should keep in mind, however, if you do plan on moving your web site.
1) Make sure the new server is just as fast or faster than your old server. Slow servers can slow down the search engine crawlers, which will cause them to leave your site sooner and index less. Have your old and new hosting company or server admin give you a report of the response time for both servers so you can compare the two and be sure that you are making a smart move.
2) Make sure the new server is not blacklisted. Although this is rare, there are times when your site's reputation can be damaged by who you share server space with. There are many blacklist and blocklist monitors out there to check a server IP with, but you can also ask your hosting company to provide this information as well to prove that the server is clean.
3) Make sure a copy of your site is uploaded and tested on the new server before finally switching everything over. Do not cancel your original hosting account until the new site is stable on the new server. This will ensure a seamless transfer, as well as prevent any issues from popping up and harming your rankings once your site fully transfers.
If you're a tech-y type and you want to get into the nitty gritty details of how to move a site from one server to another, check out this post on Matt Cutts' blog. Matt Cutts is a Google software engineer, so we trust that he knows his stuff.