UPDATE: Those interested in exploring the wonderful world of distortion correction software may also want to have a look at Image Trends' Fisheye-Hemi plug-in. This plug-in is about $30, which is much less than ImageAlign. However, unlike ImageAlign, you don't have control of the disortion correction. There is no dialog box with sliders and such. It's fully automated, which means when you launch the filter it automatically goes into the conversion. Still, it does a really great job of remapping the fisheye image while improving the overall image resolution and not distorting people who appear at the edge of the image, which is a trait typical of using rectilinear mapping programs like ImageAlign.
You can find out more about Fisheye-Hemi and download the trial version here...
http://www.imagetrendsinc.com/index.asp
Depsite it's attractive price and ability to render people in the image relatively distortion free, I would still prefer to use programs such as imageAlign for architectural structurers and other scenes not having people in them (such as in the exmple on page one). If your aim is to correct the fish-eye distortion for images that have a lot of people in them, and you don't care to have them look distorted (i.e. group photos), the Fisheye-Hemi plug-in just might be your ticket. Probably wouldn't be a bad idea to have both plug-ins installed in your machine. 