Happy buyer here.
It really saves some time when you come to deal with dialogue boxes.
Sadly enough, Windows beats Mac OS on this, offering the feature for free, built into mouse preferences, and you do can opt on it. Switching to Mac some 5 years ago, I was really surprised that Mac OS didn't natively offer such an opportunity as I expected from the best operating system on earth.
I wouldn't ever say that it has a steep learning curve, although you do need some time to get used to this behavior.
A fairly more annoying "nerves issue" I experience was striking the wrong button compulsively when in a hurry. =)
Actually, as I turned to be a keyboard shortcuts freak I must say that using esc, return, enter, spacebar, tab and cmd+D combinations on dialog boxes makes you even more efficient. But that's another story, and anyway I have to use the mouse when browsing the internet...
The new "Return cursor to original location after a click" feature added in version 2 is much welcome, squashing the only annoyance one could have catching the grip of the cursor back after the choice.
The gradient added in 2.0.1 makes a cute icon even nicer.
Works for me.