Avoiding Soft-404's for empty Drupal Taxonomies and Ubercart Categories
If you spend any time in Google Webmaster tools and run a drupal site you've probably come across a collection of "Soft-404" warnings from google. While not a critical SEO task I do think it provides just one more "signal" to google about the quality of your site.
This happens a lot if you have empty taxonomy terms (ie, terms that exist but don't have any nodes belonging to them) - for us that happens with our product catalog where products are discontinued or where a product category is imported but the products within them haven't yet been published.
Slightly related to this issue is this one http://drupal.org/node/425984 which addresses getting ubercarts categories into the xml-sitemap (and my comment at the bottom which explains how to get all/most of taxonomy to point into the catalog pages rather than taxo views).
I hacked core's taxonomy module (and have done the necessary ritual self-flagellation required of this most mortal of sins) and Ubercarts catalog module to return actual 404 responses for category pages without content. These patches are against Drupal 6.