Baltimore IEAD experience
First, there is no need to worry about the interview, actually, there is no interview, they won't even talk to you and give you and all the others iEAD in 30 minutes. So go on time, for me it was 12:30 and I went their at 8AM and had to wait. They process everyone together, i.e. pictures and distribution of cards. Didn't even checked my ID or passport, just looked at the appt letter.
Second, Baltimore will not take iEAD applications before 90 days have passed. I applied on Jan 2 for IEAD and they said that I will get a letter of appt/interview in 2 to 4 weeks, got an appointment letter on Jan 16 for an appt on Wed Jan 24th. My EAD was expiring on the 28th, very close call!
My original VSC request made on Sep 30, 2003 is still pending, even though I don't need it any more as Baltimore issued iEAD for one year.
good luck.