I wrote a while back (New NFA Retail Forex Leverage Restrictions) about new rules coming into effect from the NFA which limit the amount of leverage US member forex brokers are permitted to allow their customers. Those new rules start today. If you have a US brokerage account you have probably already received notice about the rules if your broker previous offered more than 100:1 leverage, which is the new cap.
Also, the margin must be calculated from the notional value of the position. I believe this has forced a change among some brokers who previously set their margin based on the size of a position rather than its value. For example, they would require $1000 margin on a 100,000 EUR/USD trade. Under the new rule they would have to require 1% of the value of the position be posted as margin. If EUR/USD is trading at 1.50, then a standard lot position would be worth $150,00, meaning a $1500 margin requirement.