The 16Mb 'Duo is a smaller device than the normal Memory Stick, but will come with an adapter which means that you will be able to use it in the same devices as your regular Memory Stick as well as the 'Duo specific devices.
The price quoted here is approximately 2,800 yen (or $24 which translates to £15 - Is that right?).
This is the memory device that will be used on th eagerly anticipated SonyEricsson P800, and thus will open up a whole world of opportunities for users of that, and future mobile devices.
More 'Duos with greater capacity are planned for release.