Three months ago we announced the deprecation of the legacy gadgets API. Since then we've released a legacy migration guide for converting legacy gadgets to "gadgets.*" by hand, and we're continuing to work on a migration tool to help perform this conversion automatically.
Since the migration tool isn't yet available, we've decided to delay the next step of the migration process, the requirement that all new gadgets be written using gadgets.*, for an indefinite period. So, while we still recommend using the gadgets.* API, as it will save you time later, we're holding off on this requirement. Stay tuned for another update on the migration process, with a link to the migration tool, in early 2010.