For tasks that are hidden the next day: do we ever get to see them again to keep track of what we've done?

Some ideas for future features:

A configurable break timer. The default could be five minutes - to make sure you're getting your break in between Pomodoros.

If the media player is playing music the application doesn't play it's notice that the Pomodoro is complete. It might be a good idea to either overlay the sound on top of the music, or temporarily pause the music so that you know when you're done.
Another option would be to add a vibrating alert. And possibly a configuration dialog to select between the sort of alert that you're given.

If a task has a long title it's not really easy to see the full description either in the list or when you've clicked "start" on the Pomodoro itself. A way of view the full description might be useful, e.g. double click on it for a dialog?