If you build a Mu Community, and opt for open sign-ups, you will soon encounter spam sign-ups. Usually, the newly created spam blog will be a first name followed by a short series of numbers. My first was "janelle4751" if I remember correctly. And the email domain will be something like "buyviagra.com".
The problem is, spammers have built robots to search the web for the standard text on the sign-up form. As soon as the robot encounters the standard text, it executes a little program to complete the form.
The Good Guys have come up with a variety of techniques to defeat the spam robots. If you are interested in that discussion, you can read more here, here and here and here.
Since my Mu Communities are all very, very small, and niche oriented, I've replaced the standard Mu sign-up.php page with a Google Doc fill-in form, and then I create the user accounts and blogs manually from the backend.
(My other reason for doing this was, as you may remember, that for me, at least, on a GoDaddy server, the standard sign-up.php behaved wonky in Internet Explorer... worked just fine in Firefox.... temperamental in IE.)
If I was receiving hundreds of legitimate signups every day, manually setting up each new user would be a headache. But that's not the case, and it is not what I want anyway. :-)
I am documenting the procedure of manually setting up a new user here, just in case I happen to forget how to do before the next new member comes along.
Sign in as admin.
At the Dashboard, click Site Admin. Then click Create a New Blog.
At the Blog Admin screen, scroll to the bottom, and complete the Add Blog section, using the information provided by the new user in the Google Doc form.
The new user will then receive an activation email. The new user will need to click on the login click, and sign in with their new Username and Password
After signing in, they will be directed to the Dashboard screen for their new blog. The Dashboard will only display blogs connected to that particular Username.
After signing in for the first time, the new user will then receive a second, confirmation email.
Notes for the record:
1. Yes, WordPress Multiple User still uses the previous user interface design. So, no, I am not in an old, obsolete version of WordPress.
2. Carlton is my dog.
What is a MU???
WordPress "Multiple User"
WordPress.com runs on MU. It allows many different, separate, individual blogs to exist under one installation.
I'm finding it's really useful for keeping a whole bunch of single property sites under one roof. And I really wanted to encourage all of our agents to use one of my MU communities to create individual blogs, but so far that's a little slow in taking off. :-)
EduBlogs http://edublogs.org/ for teachers and students is probably the absolute best example of a specific need or particular niche community built on a MU installation.
Active Rain itself is a similar principle: Active Rain is the host platform under which many separate individual blogs are created.