virtual subdomains vs Joomla with extensions

[BitShift]

Im looking to create a website where multiple users can have their own "virtual" sites and the url similar to "userbob.mydomain.com", which maps to "www.mydomain.com/userpage.php?user=userbob"

This should be straightfoward with Apache and mod_rewrite, however Im also considering using Joomla because all the user administration features are provided. The problem I see is there is simply too much that I dont need or want.

Anyone familiar with Joomla enough to comment on doing virtual domains with it ? Ive seen a few extensions that provide this but thats just it, they are extensions, not part of the core functionality.

comments please