This program has a wonderful amount of uses, and is a great utility.
I would agree that it has some GUI issues here and there, and could be more optimized for ease of use. THAT DOESN'T MEAN IT DESERVES LESS STARS.
I can see that there were other programs that inspired parts of thsi program.
the music selection window is similar in look to SundayPlus.
It would be nice if the user could use the up and down keys to move through the songs.
The Calendar could have a bit more flexibility, perhaps have a day view for more notes and suggestions, thoughts, etc.
Also, with the calendar page, it might be good not to have the Exit button as the automatically focused button. That's annoying to type something, hit enter, and your dropped back to the main page (which is what needs the most interface work)
One more note on the calendar page... I believe the word "Delete" has an extra T in it at the moment.
I would agree with some of the other comments that the buttons to switch between sections are a bit vague. Also, keep the different section buttons in the same place on each page. the Members button is on the left on one page, and on the right on another. Keep things Uniform. Also, keep that array of buttons on the same place on every section. Uniform placement will keep the level of confusion low, and ease of use high.
As for the term, Rota, I've never heard this term before. It might be better just to call it something more direct. I know that it'll be hard to not confuse it with "calendar", but it needs a more recognizable term. If you refer to that schedule to your bandmembers as "rota" they probably won't know what you're talkin' about either.
For the member Info, it might be nice to have it integrate with apple's Addressbook program, and the calendar sync with iCal. That would be wonderful to see how it lines up with other schedules and such.