You have until September to move all your photos.
UPDATE 17-JUN-2007: I have imported 511 pictures at Yahoo! Photos to my Flickr account. The migration tool was kind enough to mark all of them as private. However, though untagged. 🙁 I’m working through them, updating the titles and descriptions and tags. Some are being made public, some friends only, and duplicates deleted. Its over 500 pictures, so… don’t expect miracles! BTW, friends should sign up for an account so you can see the hidden 10%.
UPDATE 23-JUN-2007: I am tagging these as “Migrated from Yahoo! Photos” so they will be fairly easy to find. About half so far are remaining under the Friends and/or Family permission.