Planet Money has a fascinating story up right now about the weirdness of trying to run a pot business -- which is legal in half the country (medical or recreational) but still technically illegal federally. Banks, being federally regulated, won't make loans or give checking accounts to these businesses. They have trouble doing payroll or paying taxes. They have to run as "cash businesses" storing huge amounts of cash, paying bills in cash, paying employees in cash. They can't get loans to expand their operations. In the whole country, apparently, there are only three small credit unions, all in Washington State, who will set up accounts for the legal pot businesses, because credit unions are less stringently federally regulated.
And they're making a ton of money! The pot business is hugely popular, hugely profitable. But the banks are leaving this cash on the table.
In Canada, where medical marijuana is legal nationwide, no such problems. There are large multi-million dollar growing operations who are going from one 600,000 sf plant warehouse to SIX 600,000 sf warehouses in their first year of operation.