Since the introduction of the ALLOWED_HOSTS setting in django 1.4.4, I get a lot of django error emails to my admin address for exceptions caused by some silly spider lookin
So I typically prefer to just redirect all unmatched vhosts to a single vhost. this is done with a simple addition to the apache.conf file...
RedirectMatch ^/?(.*) http://www.example.com/$1
The example above would result in a request to any unmatched vhost to redirect to http://www.example.com, while retaining the path component properly.
This also has the added advantage of correcting the case where a user is following an invalid request or some such thing.