I want to give a user the chance to save any unsaved changes before closing a form if they did not click save . A quick test seems to show that isDirty does not bubble up to a parent.

You indicated the desire to add it to ES2008.
http://community.entityspaces.net/forums/post/6918.aspx

If it has not made it, I could override isDirty but this post suggests that some additional thought is requied as it moved into the IEntity interface.
http://community.entityspaces.net/forums/thread/8061.aspx

Any thoughts on this?

That is correct, IsDirty is not implemented hierarchically and wasn't included in ES2008. Let me refresh myself with this issue and respond back, it is still on the list for implementation however.