Note that there is a small but easily fixed problem with this component under Joomla!:

http://mamboxchange.com/tracker/index.php?func=detail&aid=8114&group_id=618&atid=2216

Users can be assigned to groups in joomla however when the group is edited the list of users in that group is blank,
this is due to a hard coded table reference in the admin.graccess.php file.

change admin.graccess.php line 137

FROM
$query = 'select * from #__users right join mos_graccess_usergroup on userid=id WHERE groupid='. $row->id. '
order by name';

TO
$query = 'select * from #__users right join #__graccess_usergroup on userid=id WHERE groupid='. $row->id. '
order by name';

The professional edition is certainly pricey but the corporate edition should be more than adequate for most non-commercial uses I think, and is much cheaper at €89. I bought the professional edition and have no doubt that it has saved me far more than €399 worth of my time!

A very polished and professional component, with good support. There's nothing else for Mambo/Joomla! that comes close in terms of features. I looked at integrating free alternatives like Eventum, but couldn't justify the time, and this one looks infinitely better, is very flexible and perfectly integrates with the rest of my support website.

All in, a joy to use - I love it!

With the core ACL enhancements still some way off, this component is invaluable for anybody wanting to separate registered users without granting back-end access, or finding that your 'special' users are special in very different ways!

Joomla! already has great potential applications beyond typical community websites, that really stretch the default CMS-oriented user groups and three-tier access level, and I think this component could satisfy many peoples ACL requirements today.

Clearly not a secure solution, but if your requirement is more along the lines of showing users only the information and functions relevant to their role, rather than restricting access, it's an imaginative and nicely implemented workaround.

However, I do have one small problem with this solution in that I cannot segregate some menus in the way that I would like (i.e. as separate modules) because I end up with some completely empty menus where the menu header is still shown. Not sure yet if it’s possible to modify mod_groupmenu to hide empty menus, or whether I will have to do this in the template somehow. Anybody solved this problem already?

One thing that I think would be nice to have in this component is a function to automatically change the standard mod_mainmenu modules to mod_groupmenu (and perhaps vice-versa). However, I achieved this with a very simple SQL command:

UPDATE jos_modules SET module = 'mod_groupmenu' WHERE module = 'mod_mainmenu'

It worked fine for me, but I don’t know Joomla! well enough to assert that this method is without risk.