leadegroot - 1:19 am on Jun 21, 2010 (gmt 0)
Because you are getting some visits, an IP problem is really unlikely - visits would stop completely.
If Google has 'decided your site isn't valuable' then bot visit frequency would drop.
So it does sound like you've been hit by the update. :(
Are you able to compare rankings before and after? (again, webmaster tools, if set up previously, will give you that)