Map Comment Authors?

Blogger does not supply the email addresses when you port the users across, they are all “[email protected]”, so it is a bit difficult to identify all the comments linked to a specific commenter.

It might be able to match the users on the username and/or website but I’m thinking that for large sites the numbers could be excessively large.

If you just want to fix the gravatars it’s possible to do that with a series of update queries, I use something like the following to fix up the missing emails on the comments I’ve made myself.

update wp_comments set comment_author_email = '[email protected]'
where comment_author = 'Andy from Workshopshed'

You could do something similar to set the user_ids.