I got the same email and was actually able to log to https://www.asu.edu/go/studentcenter/
My status was the same as tweedledee, it said my app was complete as of March 13 (the day I received the email), even though my app was complete in December (I was deferred to regular admissions from early ad).
I actually called the admissions office this morning and the told me that they sent this out to everyone... but back in November/December, they never sent out this email and my app was reviewed anyways.
I have a thread at http://www.lawschooldiscussion.org/prelaw/index.php/topic,103171.0/topicseen.html
about this very subject, and received this interesting response:
"I applied and was rejected... didn't recieve the first email. I did recieve an email apologizing for the email to which you are referring."
So maybe it is a precursor to an acceptance letter.. maybe it isn't. They didnt get the email about ASURITE, but got an apology for receiving it because they were rejected? I think that is what the poster meant. Please keep me updated if you find anything new out!! I am just as anxious to figure this whole ASURITE thing out.. it seems silly to send out an email saying "Welcome to ASU" and giving an activation code for a username when they don't EXPLAIN that it might just be for checking an application status. The email I received just gave me info on HOW to set up ASURITE. Thank god someone else is in the same aggravating situation as me. Let me know, please!