Be careful when modifying area template
Today I decided to create a new area in a Sharepoint portal. I then decided that I wanted to customize the resulting page.
What I failed to notice is that the area was created from a default template. After making some changes to this area I noticed that other area's now looked like my new area.
We have choosen to let new area's inherit from a template so that we do not have to modify all templates if we make a change. The only thing you have to remember then is to break the inheritance before customizing a particular area.