This may or may not be related but because I got here for the same redirect-loop-problem I just quickly wanna share.
I have a WP 3 multisite install with among other plugins Domain Mapping. I wanted to change the main domain. I changed DOMAIN_CURRENT_SITE in wp-config.php and imported/exported the whole database replacing all dev.domain.com to domain.com. However, somehow the home and site in wp_options always reset back to the old domain without that value being available anywhere on disk or database.
Anyhow, by explicitly adding a row in table wp_domain_mapping for the main domain, the redirect loop stopped. This should not be required, and it will probably work if I remove that row now, but I won’t try.