Quote from Gringinho:
Money in IB are safe - as good as it gets in the US, I think. They are very solid, and cater for experienced traders.
I thought the same until one of their phone brokers made a mistake on my trade that cost me over 200 pips. They've pretty much admitted fault but 2 weeks later it still hasn't been resolved, I just keep getting thanked for my "patience". Any broker that can't rectify an obvious error in this time is suspicious in my book.