The folks at BestRecipes.com.au have created a vBulletin MailChimp plugin.
It allows vBulletin forum administrators to add email newsletter subscription options to their member registration forms like this:
btw, I’ll be trying this Banana Pikelets recipe this morning. eep eep!

How is this piece working out and can you merge the same fields you have set up in vb to parse into mailchimp?
Best plugin evar. Seriously, if I had this plugin when I launched my forums, I would have a mailing list of over 75,000+ by now.
I have the subscribe option “unchecked” so the subscriber has to actually take an action to get signed up for the forum newsletter. That and the double opt in confirmation and I’m still getting 25+ new signups a day.
In reply to Jeff, I think you can pull vb fields into the plugin if you have some PHP knowledge.
I’m looking for an e-mail importer invite your friends and family plugin, similar to OpenInviter that is CMS friendly and does not have bugs in it. Do you know of one other than OpenInviter ?