I searched the site and did not see this anywhere else, so I am posting here in the event it might help someone.
Essentially, by adding some text in the UC catalog.module, you can provide to customers a description of your /store/catalog page above the Catalog display itself.
1. Open uc_catalog.module in a text editor.
2. Find line 501 or thereabouts (turn off line wrapping).
3. Look for the following bit of code:
$tid = 0;
$name = variable_get('uc_catalog_name', t('Catalog'));
$description = '';
4. In between the two little quotation marks after the <$description => you can insert some text the describes what the customer sees and how to navigate the catalog to go to the desired product page. You can use basic html tags (table, strong, etc.) to format the text. Don't get too fancy, because only filtered html will show up, as far as I know.
5. This is a nice addition, in my opinion; otherwise the customer sees a page which says Catalog and a display of product categories without any introduction whatsoever. Enjoy!