For me, FlexTime has become very useful. One of the reasons it is so useful is that I have written a few plug-ins that complement the standard functionality. For example, I have always kept a log of my working hours. It is a simple text file, written in the GNU ChangeLog style (I guess old habits really do die hard.) I use a plug-in that reads the diary file and displays it in FlexTime, providing context to the working hours spent. For me, it is very useful.
The projects Doorstop and Jupiter show up as keywords in FlexTime as shown in the image above. I can see at a glance how much time I have spent on each task. Since I write the diary anyway, I find it very useful to let FlexTime extract the tags and display them with time calculations.
I have a public Git repository for most of the plugins that I have written. I hope you might find the code useful too. The repository is hosted at Github.