enigma1 - 1:23 pm on Sep 23, 2010 (gmt 0)

You can revise the site changes in the past few months if you believe it is something to do with your site rather than competition.

Check the server logs also see if there are requests that aren't served for whatever reason. Sometimes even minor changes can affect the entire site. Check with different browsers, different configuration settings see if any errors come up when entering the site a customer.