Not yet in the UI directly but you can do this in SQL under the host /sql menu.

e.g...
SELECT * FROM {databaseOwner}{objectQualifier}Users

now, take note of the UserID for the deleted user.

Next, Run this sql...
SELECT * FROM {databaseOwner}{objectQualifier}UserPortals

That same UserID should have a check in the IsDeleted field here. To undelete them run this, but replace the UserID...

UPDATE {databaseOwner}{objectQualifier}UserPortals SET IsDeleted = 0 WHERE UserID = YourIdGoesHere

Finally, goto host / host settings & clear the cache * restart application.
HTH's,
Dave

I thought i deleted a user, but now when I try to re-create the user, I get that email address is already used on the registration page. I've searched the Users table and confirmed that the email doesn't exist. any ideas?