http://webaccelerator.google.com/webmasterhelp.html

"Google Web Accelerator only prefetches links that should have no side effects. According to the HTTP 1.1 specification, the GET method is defined as a Safe Method which "SHOULD NOT have the significance of taking an action other than retrieval." In practice, Google Web Accelerator does not prefetch links which have query parameters (i.e. have a "?" in the URL) and encrypted pages (i.e. URL starting with https://)."

"Prefetch requests include an "x-moz: prefetch" HTTP header. Websites can choose to filter out prefetch requests in their server statistics, as well as reject prefetch requests, which would cause the request to be sent only when a user actually clicks on a link. Please read the additional FAQ below for more on how to differentiate prefetch requests in server statistics."

"You can also configure your server to refuse prefetch requests by returning a 403 HTTP response code for requests which include an "x-moz: prefetch" header."