I have made my site more mobile phone friendly by detecting mobile users on the fly and serving a different layout (via triggering a different stylesheet and building the page without tables).
Google recommends that by make a site that, in their words, 'Dynamically serving different HTML on the same URL' I should change the server http header to be a " Vary HTTP header"
They say, ...
"It helps Googlebot discover your mobile-optimized content faster, as a valid Vary HTTP header is one of the signals we may use to crawl URLs that serve mobile-optimized content."
It has been suggested that if some of the pages on my site change for mobile users, but some don't, google will not like me having a " Vary HTTP header"
Anybody got any experience of this. There are some pages that rarely get visited and to make them mobile friendly is a lot of extra work!