wordpress mu domain mapping – recommendations for URLS

Just looking for your recommendations for handling the URL’s for blogs that are imported..

example:

I create a subdomain and import a existing blog – then I change DNS to point domain to my WP-MU and then do the domain mapping.

We’ll now all the URL within POST and Images etc are

http://subdomain.maindomain.com/some-url-text-etc

should I update the database to reflect to new location

http://subdomain.com/some-url-text-etc

This way the url redirect domain mapping doesn’t have to work as hard?

Thoughts?

Thanks!