The sweep's pretty new, actually - they only started doing it after the MF Global kerfuffle. The only catch is that it's not switched on by default: if you want to enable it, go to Account Administration / Excess Funds Sweep, and select "Sweep excess funds into my IB securities account".
They'll still keep enough money in the futures account (aka the "commodities account") to cover your futures margin, but everything else will be swept into the securities account so it's covered by the SIPC insurance. If IB goes tits up, the money in your futures account
should be segregated, but the money in your securities account
will be insured - SIPC insures you for cash and securities up to $500k USD total.
I think shifting your shares to SCB or DBS might be overkill unless you're over the SIPC limit. I looked at doing this as well, and the amount of hassle involved in getting dividends credited to a USD account at DBS seemed to make it not worth the trouble. (That, and I don't want to encourage DBS by paying their extortionate
thirty-bucks-a-trade brokerage.)