"On April 6th, Microsoft will release a system update over Xbox LIVE for your Xbox 360 that will allow USB flash drives to be used for storing profiles, game saves, demos and more," Microsoft's Major Nelson revealed on his blog.
"I've been testing this feature out for a few weeks, and I have to say it's really great," he added. Once you take the system update on April 6th, you'll be able to connect your USB flash drives to your console and head over to the memory section to configure your new storage device. Once you do that, the system will conduct a one time performance and integrity check to confirm the drive is working properly."
"You will then be able to configure how much storage to use on the device, up to 16 GB. The remaining space on the flash drive will be accessible by your PC or Mac. USB Hard drives may work, but like flash memory, you'll only be able to use up to 16GB of space."
You can have 2 devices connected to the console at a time, enabling up to 32GB of simultaneous storage.
Any flash drive can be used, but Microsoft has partnered with SanDisk to release an Xbox 360 branded USB flash drive in May that comes pre-configured out of the box and ready to go.