Thanks for the feedback, pianoman53 and pianowolfi ! I did consider using a keyboard-style input for this game, but the problem with that approach is that the notes range over a number of octaves - treble, bass, alto, and tenor clef with up to three ledger lines. To keep the keyboard within a range of an octave would give a misleading (i.e., inaccurate) impression of the relative locations of the notes, especially for a pianist. To spread the keyboard out over the entire range would be even more unwieldy in a speed game such as this. The flexibility of clefs is also a reason that a grand staff is not really needed, although I might consider adding it for the higher, more difficult levels.
As for game play, there is a practice mode which allows you to practice naming as many notes as you can as fast as you can for as long as you want, with the ability to change clefs on the fly. When done, the program gives you stats: percentage correct, how long you practiced etc. You just don't have an opportunity to compete against the top 10 scores.
In game mode, the only thing that gets you "out" is inaccuracy. You can go as slowly and for as long as you want at the same level, and continue to accumulate points, as long as you avoid making mistakes - five mistakes and you're done.
I realize it might take a little practice to "get into" the flow; I've found in my own testing that I'm the fastest using the computer keyboard keys (A through F are bunched in a fairly tight group on a QWERTY keyboard). Second fastest is using the iPad.
If the casual user decides the game is no fun, then I can still resort to "recommending" that my students (at least the ones with note-recognition issues) practice with it

. Perhaps there are a few bassoon, cello, or viola players out there that might find the tenor and alto clef practice useful.
At any rate, thanks for taking time to give me feedback!
Jon