Agreed, and with Adobe and Autodesk monopolizing creative software, I think we'll see more and more of this. Blender has been doing spectacularly with 3D to the point that Autodesk must be incredibly worried, and I expect we'll see more Photoshop contenders as projects like GIMP start to answer the pleas of its on-the-fence users. See the GIMP roadmap: http://wiki.gimp.org/index.php/Roadmap
Edit: And I expect as browser technologies continue to expand, we'll see more web-based competitors. In particular, with WebGL, I'm surprised we haven't seen things like all-GPU image editors to compete with the slow giants we have to deal with now.
In the mid-2000s, Macromedia started an experimental port of Dreamweaver (I think) to Linux using Wine. The project was abandoned because the market for commercial Linux applications was seen to be too limited for the difficulty of maintaining the port.
Edit: And I expect as browser technologies continue to expand, we'll see more web-based competitors. In particular, with WebGL, I'm surprised we haven't seen things like all-GPU image editors to compete with the slow giants we have to deal with now.