I figured out a work-around.
I took the e-mail address that I use for my various categories, turned them into contacts in my e-mail application (Outlook), and gave each a one-word nickname.
I can now ask Siri to send an e-mail to "Personal," with the task in the subject line, and it goes to my personal thread, or "Work," and it goes to my work thread.
This works perfectly for when I'm driving and and can't open Todoist.
ln on Feb 10, 2013 - 11:19
as someone who's still using todoist out of sheer laziness (don't feel like moving things over to another app), being able to use this feature more seamlessly is a definite deciding factor in the should i stay or should i go thought process.