spree/spree — pull request #1639 by davidnorth (2012-06-05 21:32:02+00:00)
Title: spree_users should have unique index on email

We've found we're getting a number of duplicate user records, not due to failure in the validation but some database anomaly, they have identical timestamps but sequential ids. The application is still validating users correctly. I don't know the exact cause but changing the existing index on email to unique seems like a good precaution.