Some webmasters requested that i write up a complete tutorial on creating user home pages and virtual subdomains for your members profiles. Here you go: 

Requirement: ModRewrite installed on the webserver, ask your host.

First the easy part, creating userhomepages like www.domain.com/username

Edit the .htaccess file in the root of your webserver

Step 1) turn the rewrite engine on:
[code]RewriteEngine On[/code]

Step 2) establish the rewriting base and default directory index

[code]DirectoryIndex index.php
RewriteBase /[/code]

if you have your website in a subdir on your webserver you need to reflect that like so:

[code]DirectoryIndex index.php
RewriteBase /subdir/[/code]

Step 3) Create the conditions for when to rewrite userhomepages:
The following lines say 'if the request is not a directory nor a real file, continue to rewrite it'

[code]RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d[/code]

Step 4) Actually rewrite the request.
[code]RewriteRule ^([^/]+)/?$ index.php?option=com_comprofiler&task=userProfile&user='$1' [L][/code]

You are now done creating userhomepages. Lets continue creating virtual subdomains for your users.

Requirement: DNS settings.

You first have to prepare your DNS server to allow all requests for any subdomain to go to your original website. So that means you need to see your website if you type in a rubbish subdomain like http://asdfasdf.domain.com
Not everyone is knowledgable in DNS but this is where your hosting provider comes in. Ask them to do this for you.

Step 5) Translate username.domain.com to www.domain.com/username

Below Rewritebase and above the rewritecondition add:

[code]RewriteCond %{HTTP_HOST} ([^/]+)\.domain\.com [NC]
RewriteCond %1 !www$ [NC]
RewriteRule ^(.*)$ http://www.domain.com/%1 [L][/code]

This translates username.domain.com to www.domain.com/username and does not show username.domain.com in the adress bar, as much as we would like that, it is currently not possible because joomla also uses the subdomain part to generate the login cookie. Entering the site with a different subdomain (not www but username) invalidates the cookie and thus the login. 

Now when a request comes in for http://username.domain.com the rewrite engine first translates it to www.domain.com/username and then rewrites that to www.domain.com/index.php?option=com_comprofiler&task=userProfile&user='username'

Here you can see it in action: http://tester.djtrail.nl

Happy rewriting!
~Trail.