One of the problems many users are facing when start they Joomla based site is, that the user information Joomla collects during registration is scarce - username and password often is not quite enough for their purposes. And the first reaction usually is to install a community solution, like Community Builder, JoomSocial or other, fancy user management tool - a sledgehammer to crack a nut.
Even with Joomla 1.0 and 1.5 this was an overkill in most cases, there are little neat plugins out there wich once installed, one can collect the extra info needed. One of most popular such plugins was usermeta.
Since the arrival of Joomla 1.7 the solution is ever simpler. One of the best keept secrets of the new Joomla generations is the "User - Profile" plugin. Disabled by default gets simply unnoticed by the large majority of Joomla webmasters. The plugin itself, once enabled, can add the missing extra fields you need without using any external tools. It's easy to configure even for Joomla newbies. Even better, for the geeks there is a simple way to extend it's capabilities, for details read this great tutorial.