I've used Mambo/Joomla several times over the past year and have been fairly impressed overall. Install is extremely easy, for just about everything from the base install, to modules, templates, etc. It also has a fairly good permissions system, easy built-in editing with embedded image support, support for alternate editors, etc. It has a fairly extensive user community as well, and support for integration with many major forums, galleries, etc. as previously mentioned. But I do think it's overly complex (for the sake of flexibility I think), and may be overkill for what you want to do.
I think the first thing to establish is what exactly you want to do, and *how* you want to handle it. I understand the basic desire here - create a place where people can collaboratively work on reviews. That's a fine, simple goal. My first major question is do you want all DC members to be able to contribute? If so Joomla may actually work quite well. Just give everyone permissions to edit documents at a certain level. As far as I know however this gives permissions to edit all documents of a certain level, regardless of category. I'm not a Joomla expert, but I've been so far unable to figure out how to assign permissions to an individual user or a group of users for a specific area (category or section). I know for example in LDU (another CMS) you can assign specific permissions per user or per group, and you can create your own groups. I don't know how to even create new groups with unique permissions in Mambo, or if it's even possible. Admittedly I've had little call to figure out how to do this though; there very well may be a suitable solution. But I still feel Mambo may be overkill, and I'm wondering why a "heavier" CMS like this is really being considered.
To my mind the Wiki approach seems nearly ideal. Wiki's seem essentially designed for this purpose, and unless other features of a CMS are desired, the "lighter" and more focused nature of a Wiki would be preferable. Clearly from the more complex and well-maintained Wiki's out there advanced formatting is possible, but admittedly as a Wiki newbie I haven't gotten the hang of Wiki editing very well yet. So the one thing I see lacking in a Wiki is the true WYSIWYG editor, such as those already mentioned here, or found in Joomla, etc. Wiki's just have their own system. Perhaps there is a Wiki out there that includes a full WYSIWYG editor, or support for one as a plugin? That would be worth looking into.
To my mind the permissions issue, while a bit annoying, does not seem to be a deal breaker. With the change comparison and rollback features of a Wiki, if any damage is done it can usually be reverted. It's worth trialing for a while in any case, and I wouldn't necessarily recommend leaving multiple systems open for test either, since this might dilute the content writing pool. Rather I think discussion like this and some behind-the-scenes personal experimentation should decide which system (only one, if possible) gets chosen (at least tentatively) and then a full public trial in the community for that system. If any serious problems crop up, then fall back to other solutions or research more. Above all you want to avoid having to port content.
Finally, I think an invaluable resource in all of this would be this site http://www.opensourcecms.com/
. Essentially it is a huge repository of *live* installs of various CMS's, galleries, and other content systems. Mambo, Joomla, Drupal, LDU, E107, and many, many more are up there for you to play with freely. You have full access to the admin panel, etc. If any of you CMS users have not been aware of it before, I highly recommend going and taking a look. It can't normally help you with figuring out the difficulty of the install, but as far as getting a look at the admin panel, editing, and major functionality it's really top-notch. I've found it an invaluable tool.