First thoughts: Would be helpful to have shadowed "username / password" in the first fields. I wasn't sure if those were for registering, or for logging in, or what. So that would be helpful.
Second thoughts: Love the simplicity, wish I could do more. Maybe that's not what you're going for - in which case, awesome! - but I'd love a way to go beyond the simple functions and have a simple but subtly powerful ability to do more. Fine though, can move on from there.
Third Notes: Your feedback logo is missing from the first page, just has the link. Intentional? Also, when I want to delete something, I would want something better than a "pop up" asking me if I wanted to delete it - a bit obtrusive. Better to have a fade out or something clever.
Final thoughts: Does something very very simple very well, I just wish it were less simple for my own needs. I also wish there were some quickly user-configurable style sheets to change the colors, since the shades of grey kind of mask the tasks etc and don't quite pop out in a way that makes it skimmable.
But I really like it and it seems to definitely meet the need you wanted to address!