I recently decided to use Drupal for one of my projects, since all reports are that it is both well designed and relatively easy to extend.
I'm just getting it set up locally on my MacBook Pro (10.6.7) and ran into a problem with previewing uploaded images: nothing was getting displayed for the preview, even though the images would display fine when saved.
The following errors were being logged.
The solution, took a while to find, but was relatively simple: changing the upload location to Public files (see below), cured the problem.
(Switching it back recreated the problem) -- seemed worth sharing.