...but it seems that it may actually help the big banks. Here's a link to a WSJ article that tells why:
http://online.wsj.com/article/SB1000...p_mostpop_read
For those who may not be able to read the full article, the upshot is that the cost per customer to a big bank is $350 - $450 per year. Credit unions and small banks have a cost per customer of $175 - $250.
It is believed that most of those moving money to smaller banks and CU's tend to be those with lower balances. If the smaller balances move out, the big bank's will have fewer customers, but the customers that remain will be more profitable. So, it could be that "Bank Transfer Day" is helping the big banks more than it may be hurting them.