I came across this yesterday and have been quite impressed with its customization. My previous attempts with automated time tracking through programs like rescue time involved lots of fiddling and not getting much work done. With this, after reading some notes in the documentation on Effective Use of arbtt (
http://arbtt.nomeata.de/doc/users_guide/effective-use.html) I've got a pretty useful time tracking app that's not distracting and only gives me the information I want.