If you create a new user with Twitter connect, then try to edit your profile, you get a meaningless permission error.
Instead, the system should say "please validate your email address first!".

The error you're encountering in that scenario isn't necessarily because they are in the Validating group, you can set it up so that Validating members can edit their profiles if you wanted. There's a group setting called 'Allow members in this group to edit their profile information' that is just set to No by default for the Validating group. It could just as easily be set to No for other groups that have validated their email addresses, and then your suggested error message wouldn't make sense to them.

There's a group setting called 'Allow members in this group to edit their profile information' that is just set to No by default for the Validating group.

ooh, that's some serious IPB-fu you have there. Thanks.