Getting around graphics
Once in a while I have to do some graphics work and without a doubt I believe that Photoshop is one of the best graphics software around for Windows but most people cannot afford it and have to look around for alternatives.
In the Ubuntu space, I found that the combination of GIMP Image editor and gThumb image viewer works very well for me and I can achieve all I need with those two pieces of software. I use GIMP for most stuff including layering and filtering but gThumb is good for light weight changes as it also has functions like desaturation and colour reduction. Its also good, as its name suggests, for image viewing.
I think its a question of drawing the strength of software applications but it takes some time to get a real good grip especially if graphics is a minor component of your work like it is to me.
Whilst IrfanView has been around for some time now, Paint.Net is still in beta form. Despite still being beta I think its a very good light weight piece of graphics software that most people doing casual graphics will find handy. One word of caution though is that when you install it choose custom installation and then select not to get automatic updates because last time there was a newer version and I could not open the version that I had and I could not update as well from the site and so in the end I had to uninstall it and then manually download the latest version.
Have you had a look at Xn View? I have been using for a while for simple photo editing stuff and its availble for both Windows and Linux environments.