For the last few months, when I was not busy hacking on Gwenview or other parts of KDE, I spent some time together with Sébastien Renard (of KDE France fame) creating Yokadi.
Yokadi is a command-line based, sqlite powered, TODO list. It is designed to be fast and efficient. I have been using it to manage all my tasks, including Gwenview bug reports (see "Using Yokadi as a bugtracker"). In these days of GUI applications, a command-line one might seem outdated, but it turns out I am more efficient with this tool than with a GUI or web application, especially when used together with Yakuake. Of course, your experience may vary.
Today we released the first stable version of Yokadi: version 0.9.0. If you are looking for a fast and efficient way to handle your tasks, organize them by projects, with support for keywords, urgency, due date and optional long multi-line descriptions, give it a try!
Update: Fixed the link to "Using Yokadi as a bugtracker".