Yes, the market looks like it is in for a further skid today as Greece will likely formely default on its IMF loan today. The overall impact of US dealing with Geece is rather small, but the dealings with the EU itself are rather significant. The real danger is how much the EU itslef will be impacted businesswise from the default. 

Many have predicted that the US Stock Market was in for a correction anwyay and some of this is perhaps just part of the same correction. As in many downturns, it is just a waiting game till all of the market has recovered. There is always a lot of nervous reaction as currently many peoples retirement funds are directly or indirectly invested in the market and a downturn is looked at as a real loss vs just a paper loss till you are forced to sell.