Gus Mueller over at Flying Meat Software has just released Acorn
version 1.0.  Billed as a lighter, friendlier Photoshop, it looks to
fill a niche that has recently gotten very competitive.  With other
applications such as Iris and Pixelmator on the way, the open sea
between iPhoto and Photoshop is filling quickly.

What do you think spurned all this development of photo editing
applications?  There doesn't seem to be a similar outpouring of
applications on the Windows side.  Does anyone think this might have
anything to do with developers coming to grips with Core Image, Core
Video, Core Animation,  or some combination therein?