Just tested the project and list functionality, and they don't seem to work with toodledo.com's free service, they show up as regular items on the other device. Not sure if it would be different with the premier membership. Dang, I really wanted to avoid being tied to a desktop for syncing, I like it to update on the fly. I guess I can continue to live without subtasks.
Edit: wait before you flame me. Had a vague memory, checked and realized this was all covered on the previous page. Sorry, huge launch at work this week, memory suffering.

(basically toodledo paid membership will do subtasks, sounds like.)