i got one from pittsburgh. very pleasant surprise as well. it was great, less than a week after i put them on my amcas, i got a letter inviting me for an interview (this was before they even sent me the secondary, let alone processed it). so i scheduled, went and interviewed like everyone else, and got in when they sent out all their decisions at the end of feb.
-i dont think the process is really any different if you get interviewed before secondary. you interview just like everyone else, get asked the same questions, etc. it just left a really really nice taste in my mouth, given this whole amcas crap and schools being bitches about not sending your file onto committee because "amcas hasn't sent us your verified electronic application, even though we have a hard copy of it" bull****.
-i dont think it means that it's easier, per say to get in, but i do think that it means that they score you high, initially, enough to want to get to know you. so take it as a very good sign.