Site speed will be used in Google search ranking
Google recently confirmed that site speed will be used in search ranking. Google have been monitoring site speed through Google Toolbar for past many months. If you are interested to see site speed for your site you can find in Google Webmaster Tool.
You can find more details on following links
http://googlewebmastercentral.blogspot.com/2010/04/using-site-speed-in-web-search-ranking.html
http://www.mattcutts.com/blog/site-speed/