This MarketWatch article reviews the growth of internet banks. The most interesting thing mentioned in the article are some stats:
Overall, online-only banks saw their deposits rise to $364 billion in 2012, up 32% from 2010 and more than 400% from 2004 Read more
the number of U.S. bank branches dropped by more than 750 last year, to 97,337
The online-only share of the banking industry is still fairly small, representing 4.2% of deposits. But a few key factors still bode well for Internet banks.