Me too! A watched pot never boils. We were watching the pot known as Wharton, and it obviously didn't boil. Wasn't watching this pot, in fact given their timeline I wasn't expecting to hear anything for 3-4 more weeks.
I'm really excited about this - just like you it feels great after getting no love from Wharton.
I actually had been thinking that Columbia would be a really tough nut to crack, maybe even tougher than Wharton. Columbia's admit rate is lower than Wharton's, and I have heard (from Sandy on BW) that after the ED round, Columbia's admit rate is probably in line with Harvard & Stanford. Of course, they probably don't get the same quality of applicant, and I actually don't believe it is tougher than Wharton, but it is probably tougher than any schools other than HWS and maybe Chicago this year.
It's a great feeling to get the interview, but it's really a relief knowing that my application doesn't contain any unknown grenades, at least not in the eyes of one school.
Good luck guys!