I am using Bug Tracking Systems, such as Bugzilla, Trac, etc. (and also their Eclipse plug-ins). Once they are properly installed in a server machine, they works correctly, and I know many projects use these tools to share bug & new feature lists.
However, their web interfaces are not fun to use; I have to input many things to post a bug or feature, such as priority of the bug, current program version, who to assign the task, etc. Almost all of them are unnecessary for writing code, and sometime I do not want share tribal tasks such as merely saying 'implement SomethingReader class', but without posting it, I might forget it due to some interruption of my work.
Because of these frustrations, I have recently switched to the Remember the Mlik (RTM)service to manage my bug & feature lists. RTM's AJAX-based rich web interface have some nice shortcut keys (e.g, 't' for a new task, 1, 2, 3 ... for selecting priorities), and with Google Gears installed on your browser, you can edit tasks while you are offline. And as the name 'Remember the Mlik' indicates, RTM can be used to manage quite tribaltasks; you can simply post 'write this code and that' to RTM, while this message does not make sense for the other people, it is quite informative for 'me'.
Free from explaining what to do for other people has a great effect for accelerating daily programming productivity. I'm not saying 'BTS is unnecessary', rather I'm saying BTS isnecessary for sharing bugs and features, but not for personal work management. Well-known BTSes have too rich features for the personal use. What I want to do is to take a memo at online using web interfaces I open every day, and Remember the Milk completely meets this demand.