claaarky - 8:23 am on Sep 23, 2012 (gmt 0)
I recently started experimenting with a cdn. Before using it on any part of the site our rankings were on the up, I implemented it for banner images across the site and product images for one section and within 2 weeks rankings for that section began dropping slightly. At the last Panda update rankings fell across the site by a few places.
It doesn't make sense that the cdn would cause this, but it is my key suspect at the moment. We had issues initially with browser caching - the cdn servers were overriding our cache-control settings, then our hosts enabled mod_expires which caused more havoc which we think is now sorted. One issue we were never able to resolve is that it seems impossible to control Expires dates for cdn images (at least that's what my hosts told me!).
We have a UK site on a US server, the hosts are the best company I've ever used and much cheaper than UK companies so I thought a cdn would be the next best solution to moving to a UK server.
My hosts use a third party for the cdn however, and I don't feel so confident about them or the cdn to be honest.
Whenever I've done something that slowed a page up, even by a couple of seconds, I've seen rankings drop within a couple of weeks. This makes me suspicious that our cdn is not quite providing the speed benefits we hoped for.