On occasions we have to change our hosting company for many reasons. Some common questions that arise are; will I loose my PR? Will I loose my SERPS? Here are some aspects you should be aware of while changing hosting. Theoretically you won’t loose your Page Rank or SERPS just for changing hosting. But there are some catches. Location of Server is an Important Factor First thing to note is search engines can detect where the server is located using the IP address of server. So IP address plays a vital role determining your SERPS ranking for different locations. In other words location of the server is an important factor. What makes a difference is if your domain name is a non-country specific TLD, in other words if your domain name is .com, .net, .biz, .edu, .tv, or .gov type, and you are getting new hosting from a server that is in a different country then the existing one. Its very likely that you will start getting better rank in your new hosting country, and possibly less in the previous hosting country. Minimize Downtime Plan ahead before you are changing your hosting. Test your site on the new sever moving all the files there, see if everything is working properly. Let your visitors know ahead of time about the estimated downtime. Your downtime should be as minimum as possible. If you have the site down for long time, your pages may loose SERP rankings if search engines happen to crawl the site at that time. You can set the DNS TTL to the estimated time. This will ensure that the DNS change is picked up as quickly as possible. DNS TTL is generally set as 12 hours by default. You may not have direct access to modify this, talk to your domain provider ahead about this. SOURCE: http://www.cosmocentral.com/post/2008/01/Changing-Hosting---Will-you-Loose-PR-or-SERPS.aspx
changing hosting will not affect PR, but u can lose SERPs, u need to switch between hosts fast, so that the search engine spiders don't put ur site in "URL Not found" List