Some very useful questions and answers from Business Week:

Are the deals illegal?
The IRS says so, but the courts have not yet ruled on the matter. The IRS has a mixed record in shuttering such transactions. Under what is known as the economic-substance test, the IRS has claimed that shelter deals done solely to reduce taxes are improper. But federal courts have sometimes ruled that such transactions are O.K., even if they carry no economic risk or opportunity for reward beyond their tax savings.