When i first saw this last week, I called USCIS and I will tell you that even their rep didn't know this was even though I suggested I think its the biometrics NOA/RFE. He asked for my receipt number, I provided it and he saw the status message and told me he does not know what it is but it that it is not the biometrics letter. He said it was mailed 07/26/2010, it is either a letter telling me what to bring to the interview or a letter asking me for something missing in my application. I doubted it but had no choice but to wait.
When I got it, it turned out to be the biometrics NOA/RFE as I expected, although before I ever thought it was te biometrics letter the status update wording on the website was confusing to me like as though it was something that was left out of the application that they were asking for. Perhaps this was the same confusion the USCIS rep had, but you'd think they would all have come across this before.
On another note, from reading various posts here, people seem to imply that your case is transferred to the local office after your full eligibility term is up e.g 3yrs or 5yrs. For example, I have been an LPR since 09/27/2007 with a USC spouse, currently 2yrs and 10 months after LPR. Even though my priority date of filing is 07/14/2010 and as of 07/30/2010 I have completed everything up to biometrics, does this mean that they will hold my application until 09/27/2010 anyway, to complete the full 3 years, before they transfer it to the local office and before they even schedule me for an interview? Or is it that they can transfer it to the local office anytime soon but schedule me for an oath taking only after the full 3 years (or does anyone really know any of this)?