It has been quite awhile since I was working on an hourly basis, but time tracking was everything then... the idea of web-based, mobile based and sidebar gadget based entry all seem important to me, probably the mobile component being the most essential. If you have to wait until you get back to your office to log time, that would lead to incorrect entry or no entry at all in a lot of cases. It would be important, to me at least, for everything to be available offline as well for the same reason.