phranque - 4:00 pm on Feb 4, 2010 (gmt 0)
a 301 to your canonical domain would be an improvement compared to serving all that content to multiple subdomains.
it would be better if you didn't 301 to a 404 page - i.e. redirect to a non-existent url on www.example.com.
you also have to decide what to do about wildcard subdomains.
by this i mean subdomains that don't exist and never existed.
these threads may help understand the issues:
Wildcard subdomains [webmasterworld.com]
A Records vs CNAMES vs wildcard subdomains in fail-over DNS [webmasterworld.com]