Totally agree bulbo!
One of my sites went from a PR4 to a PR3, i have a good few inbound links though!
Also referals from google went from just over 4000 in April to just over 2000 last month, and like your site - my results used to appear in the top 10 - on page 1 and have since dropped to even page 5!
I have made no major changes (any if all) to the pages mentioned - so i just don't know why this has happened and what to do!!!!!!!