There has been some concern about the potential for voter fraud with same-day registration and voting. It's a moot point - the court has ruled, and the practice is OK.
What effect has it had?
Karl Rove was just on FoxNews, and he pointed out that, in Cuyahoga County, with over 1 million voters, just 405 took advantage of the option.
So, it seems, for this time at least, very little effect. If the practice does lead to fraud, it shouldn't have any effect on the election.