ThinkProgress linked to a Reuters story which reports that Mitt Romney is in good company:

Amazon’s Luxembourg arrangements have helped it pay an average tax rate of 5.3 percent on overseas income over the past five years, less than a quarter of the average rate across its major foreign markets.
...
Had Amazon remitted all that to the United States and then paid the headline U.S. corporate income tax rate on it, the firm would have incurred taxes of more than $700 million. But it has not and the deal has allowed Amazon’s Luxembourg unit to accrue tax-free cash worth more than $2 billion.

Is that one of those "loopholes" that conservative politicians are always vowing to fix?