Listen. The man that runs IB is smarter than any 10 of those scumbags in Washington, or B school. I guarantee they dont have direct exposure to that garbage. That said, they are located on planet earth and if the entire system collapses you MIGHT have a problem. But you'll be dead at the hands of marauding mobs, so you won't have to worry. Sorry to be so blunt.
One difference between IB and the crap on wall street -- IB is mainly owned by Petterfly and a few others. They have a large stake in the firm and would be nearly wiped out (at least hurt very badly) if it went under. Thus they have a strong incentive to keep the firm from going under. None of the wall street clowns gave a sh*t if their firm went under, either way they keep their millions. Look at that ahole Fuld. He keeps his $300 million for driving his company into the ground.
I dont think the margins or broker-biz is a big problem, but they still do have considerable 'wallstreet-exposre' through their options-marketmaking? A failure of a big counterparty would still affect them, no? Also think Velocity Futures, if one of their moneymarket funds fails where they sweep customer funds, that would be problematic too? MM funds aint that safe as they used to be.
The answer to the thread's title is "as safe as possible under the circumstances." If you don't think that's good enough then there aren't many better choices out there, other than cash in the mattress/closet...
mea culpa, I read CIPF and saw CDIC. A few years back I would have laughed if you suggested that the CIPF would ever fail. I'm a little less wide-eyed now.
Money in IB are safe - as good as it gets in the US, I think. They are very solid, and cater for experienced traders.