Is there a way to allow more than one user to share the same email address? I have a couple of test accounts which could all share the same email address with no problem. Right now I am assigning each test account a bogus email address. If there is a way to enable this, I can't find it.

No this is not an option currently as the email address must be unique per account.

Yes, but what about situations where you have merged two or more forum DBs into one site, then there may be duplicates, especially if the focus of the sites were the same subject matter. Any way to look them up?

Anyone?

If you used the IPS Converters to perform the merge (which is the only real way to do such a merge without causing many complications) then the converters themselves will automatically merge accounts that have duplicate email addresses.