GIMP 2.4 Released
Enselic writes "After almost three years since the release of GIMP 2.2, the GIMP developers have just announced the release of GIMP 2.4. The release notes speak of scalable bitmap brushes, redesigned rectangle/ellipse selection tools, redesigned crop tool, a new foreground selection tool, a new align tool, reorganized menu layouts, improved zoomed in/zoomed out image display quality, improved printing and color management support and a new perspective clone tool."
CMYK colors and other functionality that keeps it from being able to replace Photoshop completely? Not to understate all the effort that has been put into it, but something like that does seem pretty basic for three years of development.
Adjustment layers. If you're not familiar with the adjustment layers that Photoshop 5 software introduced, they're layers that copy pixels from layers below them and run a filter on them, and they automatically update when the layers below them are changed. It's been said that GIMP is one of the best Photoshop 3/4 clones around.
A lot of the key algorithms, particularly for color space conversion, are patented. Guess who holds a bunch of those patents?