Note entry by count instead of duration

I'm envisioning a simple method of entering music with a mouse by displaying a timing grid of vertical lines within measures. Then clicking a particular point would enter a note at that pitch and count or fractional count. It should also be possible to drag the note to a different position or delete with a delete or backspace key press, while still in entry mode, for 'instant' corrections. The notated duration for the note could be computed once the next note or rest was entered for that voice, or default to the end of the measure. Resolution of the grid should adjustable to the typical note duration of the music. The staff might even be expandable to "piano roll" for entering chromatic passages.