I recently bought me a DSLR (Sony Alpha-300). Of course the images, taken by my new dslr are too big to publish on websites, such as picasaweb.
I used to open my windows in VirtualBox and then use Microsoft's Picture Manager (comes with Office) to resize my images to web-quality. I have to admit that this worked fine, but I got annoyed by the slow access speeds from my virtual windows to my local drives.
I heard that GIMP could be used as batch system, so I started looking around to see how I could compress my images to web-quality for multiple files. And in fact, it's fairly easy. GIMP comes with the most common Linux distributions, you only need to install gimp-plugin-registry with your package manager (apt-get, yast, yum, ...).
Once the package is installed, start GIMP. The batch processor can be found under Filters > Batch > Batch Process.
In the window that appear you can select your images, and the actions to be executed on each tab. For example for compressing images, go to the Output tab, select the image type and select a quality level.
And yet another step away from Windows :-)