My site has completely disappeared from the index, site: returns nothing and cache: returns nothing. However, link: still returns things, and the pages are still listed with PageRank in the toolbar. Google referrals have dropped to zero. This all happened very suddenly overnight.
sounds like either a ban or someone slipped up and changed your robots.txt file to disallow all (/). If not the second, check G webmaster tools and see if there is anything identified in your index status and resubmit for inclusion (once you've corrected any identified issues).