I've been setting up several Trac installations recently, and while Trac by itself is already pretty awesome (I love it's simplicity and functionality that doesn't get in the way), I was pretty dismayed to discover that administration isn't that great. Configuring Trac is a matter of (more) hacking at the command line with the trac-admin script, and user administration is managed with htpasswd or whatever authentication scheme that you choose (point being, you can't manage users via Trac itself).
Thankfully, there are some plugins that you can install to alleviate the situation. Trac itself publishes the WebAdmin plugin, which is slated for inclusion in Trac in Trac 0.11. This adds a web interface to trac-admin and it's pretty darned useful when used with two other plugins: Account Manager plugin and WebAdmin Users plugin.
Account Manager plugin adds HTML form-based login instead of the default HTTP authentication with plain olde Trac (plus user registration and changing of passwords). I'll let you in on a secret - I never managed to configure my Trac installs properly to use HTTP auth, but with this plugin it just worked.
The WebAdmin Users plugin let's you add/remove users via WebAdmin plugin.
By the way, if anyone has got a Linux binary for mod_dav_svn.so for Apache 2.2, let me know - I'm too lazy to go through the whole trouble of compiling it.