I just had a play with Asana, which is great in many ways.
But doesn't support a hierarchy other than Project->Task. As I frequently want to break things down into much smaller chunks and subchunks I guess I'll be sticking with Workflowy for the moment.
Exactly, I replaced Asana with Workflowy for this reason.
The other showstopper for me was that Asana's mobile site is almost unusable outside of a fast wi-fi connection. Workflowy is extremely usable from a phone even when I'm in an area with weak bandwidth. So I can take notes and start planning while in a meeting and they're on my screen when I get back to my desk.
But doesn't support a hierarchy other than Project->Task. As I frequently want to break things down into much smaller chunks and subchunks I guess I'll be sticking with Workflowy for the moment.
Shame, really. It's got a great interface.