While we wait for a Mac App I would like to share a workaround for a feature at the top of my list: Universal Task Add

Setup:
1. Set up RTM with you twitter account
2. Download and install Twidget.

Add Tasks:
Launch Dashboard, direct message RTM, type your task
or,
F12, d rtm "your task name"

-Twidget will already be selected if you used it last. So no need to hunt and peck with the mouse. Smart Add works for this too.

Links:
https://www.rememberthemilk.com/services/twitter/
http://gettwidget.com/
https://www.rememberthemilk.com/services/smartadd/