Pivotal Tracker [1] was amazing for my team. My team was spread all over the world, and it was hard for us to even schedule a stand-up for everyone because of time differences and other conflicts, so having a site that we could all get to was crucial.
Even when it got to a point in the project where it was just me tracking my own tasks, Pivotal worked better for me than post-it notes could possibly have. Among other things, I ALWAYS had access to them where I needed them -- at my computer.
I love PT and it's amazing for task management and reporting on a day-to-day basis, however it's not good at managing the big picture where I think cards on the wall is really good for exactly the reasons Daniel mentions. For remote use I don't think there will be any good software solution until 20' high-res touch screens are readily available :) In the meantime I use Writeboard.
Even when it got to a point in the project where it was just me tracking my own tasks, Pivotal worked better for me than post-it notes could possibly have. Among other things, I ALWAYS had access to them where I needed them -- at my computer.
[1] http://www.pivotaltracker.com/