tsdpsg - 4:12 am on Mar 11, 2003 (gmt 0)
carlr, if all your interior pages were PR3-4 and just dropped to PR0, then I'd say you need to be concerned. How many pages were dropped to PR0?
Make sure you cleaned everything up that would be considered against Google's TOS. Continue to make valuable content pages and get relevant reciprocol links pointing back to your site.
If it is a penalty, the next deep crawl will hopefully see that you've cleaned it up and give you your PR back.