In order to get hign PR, last month I add link swap script into my page,after one week,the page has disappeared from google indexed. So pay attention when you add some SEO script into your oage
maybe if they felt it unfair or "beating the system" they would remove your site. Hopefully after you remove it you will be back on the engine fairly quickly.
I had the same problem actually , my site was suddenly removed from google . Next day i came it has 100 pages indexed and now its back to 750 ... What was the reason for it , i still dont know - but everything is okay now