The Help for the Social Security Benefits Worksheet in the CD/Download TurboTax software says if you are a U.S. citizen residing in Canada, do not enter the amount from box 5 of your SSA-1099. It doesn't say anything about needing Form 8833. Apparently they think it's okay to just omit the income, and not show it on line 6a.
I don't think that omitting it would cause any trouble. The IRS knows it's not taxable. They don't go after people when they can see that they are not going to be able to collect any additional tax.
