Magento

If you have any problems (column not found e.g.) please rebuild the flat product catalog under System > Cache Management first.

You can specify a default for all categories and products under
System / Catalog / Customer Groups Catalog

There you can also choose to disable the extension.

The default after installation is no categories or products are hidden.
You can override the default from the configuration in the Product Management
and Category Management pages.

This extension is a lot more flexible then the Netzarbeiter_LoginCatalog and
Netzarbeiter_CustomerActivation modules, but it is also more complex.
I suggest not installing this extension together with Netzarbeiter_LoginCatalog,
as that doesn't really make sense.

Release 0.2.5beta and above works with and without the flat catalog enabled

If you ever uninstall the extension (I don't hope so ;)) your site will be broken, because Magento doesn't support
a mechanism to remove attributes with an extension, and this extension uses source models.
To fix the Error, you have to execute the following SQL:

DELETE FROM `eav_attribute` where attribute_code like 'groupscatalog%';

DELETE FROM `core_resource` where code = 'groupscatalog_setup';

Don't forget to clear the cache, afterwards.

Dataflow:
Check this post for information on how to get it to work (thanks to sosuke!):
http://www.magentocommerce.com/boards/viewthread/28303/#t103506

TODO:
- Add option to redirect to a configurable URL if a hidden product/category is loaded (Thanks to Did for the idea). This will be a while until I have time to get it implemented, so don't count on it soon.
- When all products in a wishlist are hidden, show the "No items in wishlist" template instead of an empty grid.

0.3.2 Make extension work with SOAP/XML-RPC API calls
0.3.1 Dutch locale (nl_NL) added, thanks to Dirk Dinnewet!
0.3.0 Make "Select All" Checkbox in Visible Products Grid usable
0.2.9 Update product attribute backend model
0.2.8 Fix bugfix from release 0.2.7 *sigh* Sorry about that
0.2.7 Fix bug in customergroups source model when saving a product after adding it to a new category (Thanks to Don Gilbert!)
0.2.6 The Edit Customer Page has a new tab to enable/disable product accessibility for the customers group. Also, if enabled in the config section the db field size can be dynamically resized if required for complex permission configurations with 20+ groups. Thanks to Liana DiCicco for sponsoring the development.
0.2.5 Magento 1.3.1 compatibility issues (more to come with one of the next mage releases... had to work around awkward implementation quirks)
Release Release 0.2.4 fixed layered navigation translation namespace (thanks to Julian Bakalov for the bugreport!)
Release 0.2.3 add compatibility to the flat catalog in magento 1.3
Release 0.2.2 added French locale, thanks to vacmar!
Release 0.2.1 try to keep compatibility with Magento 1.1.8 for a bit longer (thanks to Mark Walsham for reporting)
Release 0.2.0 uses a better way to fix the issue fixed in 0.1.9 :)
Release 0.1.9 fixes a bug with the global scope category names being used instead of the store view settings (thanks to Julian Bakalov for the report!)
Release 0.1.8 clears the layered navigation cache for products if the groupscatalog config was changed
Release 0.1.7 fixes the block caching of the layered navigation
Release 0.1.6 fixes the layered navigation
Release 0.1.5 fixed sitemap generation - now uses settings for not logged in customers.
Release 0.1.4 fixes the advanced search bug, and features a rewrite of the filter logic
(smaller code base and better compatibility with other modules)
Release 0.1.3 fixes compatibility with Magento 1.1.7 and above
Release 0.1.2: Fixed bug introduced with 0.1.1 (bad start here, sorry for that. Thanks to Tom Arnst for notifying me)
Release 0.1.1: Navigation block caching fixed

If you have ideas for improvements or find bugs, please send them to vinai@netzarbeiter.com, with Netzarbeiter_GroupsCatalog as part of the subject.