Robert Scobles (read a nice Economist.com article on Robert Scobles) reaction was:
When I got called over to meet with Brian last Friday I had no idea what was coming, other than he wanted to talk to me about “new file formats.” I thought back immediately to the pain we had when Office had changed formats in the past. I used to have to remember to save as an older format when emailing files around the office until everyone else got up to date. So, I started the interview with “are you nuts?” But, Brian won me over. By the end of the interview I was floored. “The Office team is doing this?” In my mind Office was always associated with format lock-in and a closed, proprietary approach. But now I can see EVERYTHING inside the new files. Wow. Wow. Wow. Wow. Congrats to Jean Paoli and Brian Jones and the entire Office team (Steven Sinofsky was behind this too). This changes everything. Oh, and one end-user benefit? The new files saved with the new XML format are about 1/4 the size of the existing binary format. Listen to the video to hear why that is.