Quote from Hurricane:
I'm a heavy forex trader with IB (but not having traded forex with other brokers, can't compare IB to others). With IB, there are no lots. You indicate the amount of currency you want to buy and the currency pair (e.g. buy 54,615 EUR.CHF). If you don't have the currency you're purchasing with, a margin loan is automatically generated. Interest earned on the long currency and owed on the short currency is accrued nightly. Otherwise it's pretty straight forward.
Spreads are very tight. Commissions are low. Price improvement on limit orders is routine. Apart from the occassional execution against another IB customer's order, IB does not take the other side of the trade, so you're buying/selling directly with the liquidity providers (e.g. Deutsch Bank).
To me, IB operates with complete transparency which seems to be in short supply in the retail forex world.