I've never quite understood what the purpose of a contribution form was for a post-tax contribution to a Roth IRA. I'm not getting a deduction for it or anything, after all. Is there any consequence if a person were to forget to document a Roth contribution in income tax filings?
From the IRS instructions for Form 8606:
Penalty for Not Filing
If you are required to file Form 8606 to report a nondeductible contribution to a traditional IRA for 2010, but do not do so, you must pay a $50 penalty, unless you can show reasonable cause.
If you overstate your nondeductible contributions, you must pay a $100 penalty, unless you can show reasonable cause.
From my personal experience I did not have to show any documentation for a Roth contribution, since its being done with post tax dollars. And once the money is in the Roth it anyways completely sheltered from future taxes. I file taxes using Turbo Tax and I have a Roth account since the last few years.