Does it matter? Well not right now, not until you have the community setup.

Once things are up and running though performance would almost certainly be better if you were using a database - since you'll be wanting to display things like username, last login tim, profile details, etc.

It just makes sense to me to use a database - especially because I'm assuming you'll have to store login names and passwords anywhere. A database is designed to get fast at queries and to link things together.

Maybe something simple will get you started, something like this:

CREATE TABLE `users` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(25) NOT NULL default '',
  `password` varchar(32) default NULL,
  `email` varchar(75) default NULL,
  `joined` datetime NOT NULL default '0000-00-00 00:00:00',
  PRIMARY KEY  (`id`),
  KEY `username` (`username`)
);

CREATE TABLE `user_info` (
  `userid` int(11) NOT NULL,
  `profile_text` TEXT default '',
  `location` varchar(30),
  `age` int default 0,
   ...
   ..
);

CREATE TABLE `user_preferences` .. ;

CREATE TABLE `user_friends` ... ;
[download]

Then you can run a simple query to get the profile text, age, etc, from the user_info table, and all the other details from any other tables you might create.