In the Statistics section of Googles webmaster tools (previously sitemaps) they allow you to "Download all query stats for this site (including subfolders)" - I am trying to find out what time period this covers but have not had any luck so far - if anyone knows the answer it's be much appreciated
Thats a very difficult one to track as the time frame seems to change quiet alot. Recently the stats had been stuck for over 3 weeks but I would guess that was down to Google tinkering with the back system.