Old School is a class of people favoring traditional ideas.
In other words, the old proven methodologies are still the best. The people believing in 'Old School' are hesitant to accept new ideas, new methodolgies or new technologies.
A very good example of this is the Quartz watch. This is clearly explained by Thomas Kuhn @ Skepdic.com, to quote:
The Swiss failed to patent or market the quartz watch, even though they invented it, because they couldn't shift paradigms. They couldn't shift paradigms because they couldn't see that there would be a market for another kind of watch besides the kind they'd been successfully making and selling for generations. The Japanese made all the money from the quartz watch because they didn't have an old paradigm that locked them into a way of thinking that precluded patenting and marketing quartz watches.
Paradigm shift is a change from the fundamental model of events. It has been widely applied to other realms of human experience as well.
There are many cases of paradigm in modern business strategies. Those who can shift to a new paradigm succeeds and those that that remains in old school fails.
I remembered from my past workshops about paradigm when I read this post in Drupal Template Framework. Old School Drupal just don't want to accept that there are new ideas for the Drupal CMS. Reading through the comments made me think how unpleasant Old School Drupal is in providing comments to new ideas.
I know that this post will trigger a backlash from the Drupal community. I am not against the Drupal Community, I am just giving my personal thought on the particular post and comments mentioned.