Drupal Theming: $path vs. base_path and path_to_theme
When developing Drupal themes, there is one bit of code you type over and over again:
sites/all/themes/blueprint/images/whatever.jpg
Where images/whatever.jpg could be a css file, or other file, but is normally an image.
However, since clean URLs in Drupal appear to make fake directories, the web browser thinks your image is located in:
node/345/sites/all/themes/blueprint/images/whatever.jpg
When it's not. Luckily Drupal has tools to help you in this case.