Paul Jensen has created a new Operations Research blog for his Operations Research Models and Methods studies using Microsoft Excel and VBA. Jensen has a great website devoted to instructional Operations Research Modelling Methods developed using the Microsoft Excel spreadsheet and VBA. His main website, Jensen's Operations Research Models and Methods, is very well laid out with modeling tools and instructional descriptions on a number of Operations Research models.
Now you may be wondering why I would endorse Paul Jensen as someone who advocates Open Source software. My main focus it to promote tools for the Operations Research community. Paul Jensen provides these tools to the public domain. His website is full of Operations Research instruction and detailed case studies. Dr. Jensen is doing a great service to the field of Operations Research and I hope he continues to provide wonderful resources.
As an aside I would love to see the same type of devotion to OpenOffice Calc as Paul Jensen has to Excel. I hope someone with the same spirit could start a similar project.