It's a Drupal and PHP best practice to develop with E_NOTICE turned on. Please do.
I installed a new contrib project from Drupal.org yesterday and found a whole bunch of warnings emitted to the screen. It turned out that the developer of the project had not (apparently) been working with E_NOTICE properly enabled in their development environment and so had never seen these. Two of them were actually obvious logic failures. You want to know when PHP is complaining about your code! (Make sure you have error/warning reporting to screen turned on during development too!)
So here's the deal: PHP has a flag called E_NOTICE. In release version of Drupal it's ignored (in includes/common.inc, drupal_error_handler()). In dev versions of Drupal and in Pressflow it's enabled. Anybody who ever edits PHP code during development should have this turned on. So you can
- Use a development version of Drupal
- Use Pressflow
- Or apply this patch to your Drupal stable install (works on D6)
Why does this matter to you? Because if you make a single mistake, like using a misspelled variable, you won't know about it! You might do something like:
$x = $varable;
by accident, just a simple typo. If you have E_NOTICE enabled, you'll get a complaint and can fix it right away. If you don't, you've introduced a hard-to-find bug.
What about contrib modules/themes that have warnings? Well, we need to get them fixed. Please, fix them up. We wouldn't have this problem if all if everybody did what's promoted here. But it's easy enough: Fix the problem and file a patch. That's what I did last night.
Please everybody: Run your dev environment with E_NOTICE, and fix problems when you find them. Let's make contrib and our site run clean.