As a part of the Tax Increase Prevention and Reconciliation Act of 2005 (TIPRA), income limits on Roth conversions were repealed, starting in 2010. However, while TIPRA removed income limits for Roth conversions, it did not eliminate the income limits for new Roth contributions.
As a result, a new creative use of Roth conversions opened up: just contribute to a non-deductible traditional IRA, and then complete a Roth conversion immediately thereafter. Since neither transaction individually has a contribution limit, the client can still get money into a Roth IRA each year, regardless of the still-remaining income limits on Roth contributions. The end result: accomplishing a "backdoor Roth IRA contribution" for someone who wouldn't normally be eligible to make a Roth IRA contribution in the first place.
There's just one problem: the IRS can still call a spade a spade, and the rising abuse of this backdoor Roth IRA contribution "loophole" may bring about its permanent end.