When you move a site to a new host, does it have any effect on SERPs? I've never previously moved any of my sites, but I'm considering moving a site from my reseller host to a completely different host. Will the move have any implications for me?
As long as it's done properly (without any downtime), you should be good. I would setup the stuff on the new host and set the DNS servers to point to the new. Leave the old site running for a week or two for all the old DNS servers that have the IP address cached. Then take down the old.
Will having the old stuff still available have any implications of duplicate content? Or will the BOTs just find either the new or the old, but not both?
before you change the host, make sure you download all your webpages through ftp. Also you need to save your databases, if you have. Then change the dns, and upload all your stuff as it was... Enjoy...