
Does what it says it does, with a couple caveats
First off, I'd like to compliment the developers here for being so focused and responsive during the creation of this module. I think this is probably the best documented Drupal module I've used, and it does what it says it does: allows you to use a single code-base across multiple domains and sub-domains, plus, easily create critical exceptions.
The way it does this is a little tricky, and my main useability compliant is that it really wants you to make system-wide changes in the primary domain, but doesn't force you there. Consequently, in the heat of the moment, its pretty easy to make changes you think are system wide, that aren't, and conversely, make configuration changes you think are subdomain specific, with interesting results.
Once you get the hang of it, it works very very well. Except for one upgrade early in the dev cycle, the module upgrades have been exceptional for how well they don't "break" things.
For certain kinds of projects, this module is/will be critical for implementing a straightforward, well-managed configuration and administration process. This should be incredibly useful for any medium-sized enterprise, with well defined departments, or any kind of organization who has tight- to moderately-tight relationships with affiliates. It probably won't work for organization with loose affiliates.
I haven't used it with Organic Groups, and suspect that might be an interesting can of worms, but for what I've been using it for, it's an excellent module. And when I've had problems, it has been easy to find the explanation and fixes in the documentation, (which, in my humble opinion, should be the gold-standard for Drupal module documentation).
Review by trailerparkopera [info] on October 21, 2008 - 11:01

Domain Access can revolutionize affiliations
Addendum since initial review: I have completed a simple example website using the Domain Access module. So far I installed the module, the helper modules I needed, figured out how to implement wildcard DNS so the subdomains are automatically added to the site, and installed the Shared Sign-On module. Next I will demonstrate how to use Organic Groups and Domain Access together. I mean to create a screencast in the near future as well and will update this review when that is complete.
I've been testing Domain Access with multiple domains, both second-level domains (e.g., example.com, examples.org) and subdomains (e.g., sub1.example.com and affiliate.example.com). I haven't found a client that is in need of affiliate web sites, but I have a few in mind that have wanted affiliate driven sites attached to there main website in the past. So, I'm hopeful to give a real world example in the future.
The main example given by the developers is www.skirt.com. If you visit that site you can see Domain Access in action with the choose another skirt drop-down menu.
Essentially the "Domain Access project is a group of lightweight modules that provide tools for running a group of affiliated sites from one Drupal installation and a single shared database."
The module is both easy and difficult to install and use, and depends on your needs how many of the helper modules you'll need, and what your level of DNS and sever experience you have. I already operate a dedicated server and understand dns pretty well. Conceptually I think it will be difficult for newbies, but the installation is fairly simple for seasoned developers. The Documentation is first-class and maintainer agentrickard is on top of the modules needs and tickets.
Using Organic Groups and Domain Access does work together but I found the need to follow this issue to make it work well: Anonymous user permissions when integrating with OG.
I've found most helper modules that are included to be essential, such as Domain Configuration, Domain Content, Domain Navigation, Domain Prefix, Domain Theme, Domain Views. I especially like the fact that Domain Prefix provides "enabling select database table prefixing for use with subdomains." So for instance each subdomain can have their own logs (watchdog). The user interface isn't too shabby either.
I'll post something more here once I either have a client with this need, or set up an example website.
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Scott Blackburn | Web Developer
Droplits: Sustainable & Systemic Web Solutions
If you are looking for help with Drupal modules and themes, and any Drupal website development contact me at http://droplits.org/contact
Review by designdivide [info] on June 13, 2008 - 23:19