The details of the report were very accurate. USB hard drives or flash drives may be used, but will require at least 1GB of space. Any space to be used for Xbox 360 storage will have to be partitioned and formatted. Up to 16GB may be partitioned on a single USB device and two can be attached at a time for 32GB of storage.
The Xbox 360 will run a quick test on your device to determine if its meets the requirements before formatting. Microsoft recommends using flash memory as hard drives with spinning parts will have slower performance.
The functionality will be released through a Dashboard update on April 6. Additionally, Microsoft and SanDisk will be partnering to release pre-formatted, ready-to-go flash drives to be used as Xbox 360 storage in May.