From a grad student in our department who used to work at the FEC:
bq. Anecdotally, of the 300 committees I reviewed at the FEC, only one corporate PAC made independent expenditures over $5000 in the 2008 election and it was the Human Rights Campaign, which is a non-profit corporate PAC. The rest were unions (AFSCME, SEIU, etc.). I think labor unions are going to take much greater advantage of the decision than corporations – especially when it comes to things like GOTV drives and voter contact communications. I think the types of corporations that will get involved with that type of activity are the non-profit interest groups (Human Rights Campaign, NRA, Chamber of Commerce, etc.) as opposed to for-profit corporations like Goldman Sachs and Bank of America.