Honestly I've never found a good service / app for handling todos. I start well meaning enough, get some lists with stuff I need to get done then they slowly get out of date, I stop using it and then I'm looking for something else a few weeks later.
I wish more to-do apps integrated better with calendars. It's almost always shitty integration if it even exists.
I wonder if this space is ripe for disruption if someone can find a way to keep people engadgrd and up to date with their lists. Maybe it wouldn't even be a list of sorts? Hmm. Just thinking out loud here.