A couple of members of this forum (dnyc and nyker) both sent in their N-400s on 12/27/07, and have already received their ILs. Myself, Vik Pal, thrix, and a couple of other members have applied at around the same time and had our name checks cleared. We're still waiting for ILs.
Just when we think we have finally figured out how the USCIS works, something like this happens and blows a big hole in our theory. Technically, if your background check is done, you should be given an interview, even if there are people with earlier PDs, but still have their background check pending. Apparently, that's not always the case.
When I went to InfoPass, the IO explicitly stated that my background check has been cleared and I've been placed in queue for interview. What I think your IO meant to say is that you've been placed in queue, and it will take up to 90 days for your interview to scheduled. It's a fact that service centers schedule the interviews, not the DOs. The service center has a list of available interview dates and times for all DOs in their jurisdiction, and schedules the interviews on the basis of that list. Once the interview has been scheduled, your case is then transferred to the DO.
Thanks Bud, you are AWWWWWWWWWWESOME!!! Sucks that I have to go and check my PO BOX even on Saturdays...