The first thing I thought when I read http://www.asktog.com/columns/022DesignedToGiveFitts.html was this awesome game.
I really think that it's the perfect idea to consider for osu!, because it has such a direct effect upon the ease of gameplay. Osu! is all about moving your mouse and clicking to a rhythm, so anything that affects difficulty is important to utilize.
More or less, I see a few different ways in which it is applicable and may be useful in making this game's difficulty more dynamic.
First of all, Fitts' Law:
- The further a target is from the mouse, the larger it must be to retain reaction time.
Among the various possible implications, here are a few implementations which you could use:
An option in the editor to dynamically increase the size of targets according to distance
As distance from last target increases, the next target's size is increased by a factor chosen in the editor. Likely, an increase of 10 pixels in diameter per 100-200 pixels distance would be reasonable. The exact distance before the increase should be selectable and also disabled for harder songs. Essentially, this is for easy mode.
A mod to increase target size by distance, rather than an option in the editor. If implemented as a mod, then the hard version would decrease target size. With these mods, the change can't be too noticeable; just enough to subtly aid or hinder the person (and maybe exaggerated versions which are quite drastic and give increased rewards).
I've been playing this game and so far it's absolutely wonderful! You've done an excellent job on designing the menus; it feels completely natural and I have a hard time finding anything done wrong
I feel that not only is this game done the way it should have been, but also that it has a polish I rarely see in other games, especially in terms of the controls. I'll be honest, I suck at this game, but it's been remarkably easy to improve. It's made so well in fact, that the majority of my problems now are just that my computer lags; when I began a week or so ago, I couldn't even finish an easy song. I'm already onto the slower hard songs 
Anyways, I figured that you might be interested in Fitts' Law because it's incredibly useful for controlling this game's difficulty ^_^
I really think that it's the perfect idea to consider for osu!, because it has such a direct effect upon the ease of gameplay. Osu! is all about moving your mouse and clicking to a rhythm, so anything that affects difficulty is important to utilize.
More or less, I see a few different ways in which it is applicable and may be useful in making this game's difficulty more dynamic.
First of all, Fitts' Law:
- The further a target is from the mouse, the larger it must be to retain reaction time.
Among the various possible implications, here are a few implementations which you could use:
An option in the editor to dynamically increase the size of targets according to distance As distance from last target increases, the next target's size is increased by a factor chosen in the editor. Likely, an increase of 10 pixels in diameter per 100-200 pixels distance would be reasonable. The exact distance before the increase should be selectable and also disabled for harder songs. Essentially, this is for easy mode.
A mod to increase target size by distance, rather than an option in the editor. If implemented as a mod, then the hard version would decrease target size. With these mods, the change can't be too noticeable; just enough to subtly aid or hinder the person (and maybe exaggerated versions which are quite drastic and give increased rewards).I've been playing this game and so far it's absolutely wonderful! You've done an excellent job on designing the menus; it feels completely natural and I have a hard time finding anything done wrong
I feel that not only is this game done the way it should have been, but also that it has a polish I rarely see in other games, especially in terms of the controls. I'll be honest, I suck at this game, but it's been remarkably easy to improve. It's made so well in fact, that the majority of my problems now are just that my computer lags; when I began a week or so ago, I couldn't even finish an easy song. I'm already onto the slower hard songs Anyways, I figured that you might be interested in Fitts' Law because it's incredibly useful for controlling this game's difficulty ^_^