I love Trello, simply because it's such a generalized way to organize thoughts. I use it for everything from project outlines to detailed to-do, to-read and to-watch lists.

One thing I've found convenient for my high priority to-do card is a script that prints it on to my desktop. Trello already has a fairly solid API.

In my opinion the biggest challenge for to-do solutions is how to stay in the users face all the time. Which is probably why sticky notes on the monitor are still popular.

I use trello in this way too and find it works fairly well.

One gripe I have is that it's a little hard to go back and look at what you've done over the years, at least with the way I do it: I have a To Do (Planned), To Do (This Week), Doing (Today), Done (Week yyyy-mm-dd). I archive the Done list for the week at the start of the next week.

Pulling up done lists for the last few weeks has been ok, but I'm not sure if this solution will scale well.