The Alternative PHP Cache (APC) module was enabled on our production webheads last night (2/7/12). This was done to decrease page load times and increase capacity. The average load time on the homepage has dropped from 33ms to around 9ms and has halved the requests to our back-end file servers.
There are some side effects to this this improvement. The first being some sites don't behave well being cached. Another is modification of static (non-Drupal) sites will not be immediately visable on our production infrastructure. In the short term the fix is to create (or edit) the .htaccess of the site having the work done and add this line too it "php_flag apc.cache_by_default 0" this will prevent APC from caching the site. The long term solution will be to fix the sites to get them working correctly with caching and to move development off of our production gear and into a proper development environment.