A Path For Ron Paul
Let's say Sheriff Joe Arpaio of Arizona succeeds in getting Obama off of the ballot in Arizona. This could have a snowball effect on other states.
This situation could potentially leave the Democrats without a candidate on the ballot for November if the timing is right because they might not have the time to submit a replacement. This would be true after the week of September 3, 2012. They might not be able to legally put someone else on the ballot.
This would give Ron Paul the perfect opportunity to run as a third party candidate because Democrats who are looking to make sure Romney doesn't get in the White House would prefer to vote for Ron Paul (in general). Also, Ron Paul would take a large chunk of Republican voters anyway.
I realize it would take a lot of events happening at the same time to make this happen but it is a possibility.