The has been updated version 0.5.6.
This release fixes some database schema inconsistencies from previous installations, and also fixes an discrepancy between the button type selections on the product form and the values expected with the product is saved.
New in 0.5.6 is quantity tracking for all product types, with per-product options for handling out-of-stock conditions. Products can continue to be sold (backordered), hidden from the catalog, or displayed but with no purchase options.
New product detail templates are included. If you'd like to check out the new layouts, manually edit "paypal.php" in the plugin directory and change $_PP_CONF['tpl_ver_detail'] from "v1" to "v2" near the bottom of the file. A future version will offer the selection as a configuration item, or possibly on a per-product basis.