Today we've had to update some nicknames to make them unique. Before
today's update the initial nickname for a new user was calculated
using the name part of the email adress. This caused some troubles for
users with the same name part but different domains (see
http://code.google.com/p/rietveld/issues/detail?id=99 for example).
Only a few accounts were affected by this change and they've been
informed by email (so if you've received no email, your account hasn't
changed).
Sorry for any inconveniences!
andi