I think you should take a leaf out of basecamp's book and make it super easy to share tasks with random people. People shouldn't have to subscribe to be able to "do" and mark compete/comment on tasks i assign them. This would then enable users like myself to migrate away from basecamp more, and it would spread the word about toodledo more as i would be assigning adhoc tasks to dozens of people who would otherwise know nothing of toodledo and who i'm not going to sign up just to tick a few boxes every now and again.
The reality is that not all people work in tight knit small teams nowadays, often they'll be working with dozens of people across several countries working loosely and just needing to assign and share responsibilites... toodledo could step up to the plate in this regard.
I reckon a lot of people are like me and only use basecamp as a glorified team task list.
Otherwise, awesome product. I'm a fully paid up pro member and think its work every dollar.