Google has said this before but it is always comforting hearing them say this multiple ways.
Google's Zineb Ait Bahajji said in a Google Webmaster Help thread that if done correctly, there will be "no negative impact on the website's visibility in the long term."
She said this is in Google's documentation:
As the documentation explain very well, if the site move is done correctly, it will have no negative impact on the website's visibility in the long term.To quote the article : "[T]he visibility of your content in web search may fluctuate temporarily during the move. This is normal and a site’s rankings will settle down over time."
"Settle down over time" doesn't necessarily mean "no negative impact" but since Zineb is making that 100% clear now, it is good to share with you all.
Google: "if the site move is done correctly, it will have no negative impact on the website's visibility in the long term."
How can you do it correctly? Well, Google has a very detailed document and walk through on their help section.
Forum discussion at Google Webmaster Help.
