Page Speed or site load time is an important factor in summarizing user experience. It also has an impact on the site's search engine results placements too. How Google determines site speed and what number of sites' ranking is affected by site load speed, was what the webmasters wanted to know, and this was addressed by Google's Matt Cutts in a video.
Among many other things, Matt said that approximately 1 out of 100 searches are affected by the site speed ranking factor. He said and we quote, “that it would actually change the ranking to a noticeable degree.”
In this video posted on the Google Webmaster Central Blog, Matt Cutts stated that the site speed factor affecting the site's ranking comes to 1 in a 1,000 sites. The bottom line: About 0.1% of the websites have page speed problems that affects their rankings.
The video offers some further insights into how Google determines page speed. Do leave a comment once you listen to all that Matt Cutts has to say.