30 Aug 11 5:12 pm
If you are changing hosting provider for your website, in theory the change would be seemless. You make the change and depending on the TTL (time to live) set in the DNS records, some DNS servers will point toward old hosting, some to the new. This isn't normally a problem but if you are running something like a forum which can get updated in between the change, you may want to put up the maintenance page whilst you move the site.
I don't think changing a host would effect SERPS, google ranks domain names not IP addresses or locations of hosting providers, although a host that is close to your target market will decrease page load