I don’t know how the talks were to the participants, but I gave a talk at Wellesley College and then at an Internet Conference in Moscow, both via Skype. It certainly worked for me even though the Russian one was at 2:30AM. With the one at Wellesley, I gave the talk by showing me at first, then my slides (by screen share), and then me for Q&A. They said they were happy. On the Russian one, it was a 15 minute Q&A with a moderator. I never saw the audience there, so that was a bit difficult. I have heard the Tim Berners-Lee does most of his talks remotely.
When I totaled my “carbon footprint” the biggest issue by far was air flights. I know that there is nothing that replaces face-to-face, but the time and stress it takes to travel costs and costs.
Flying is one of the most magical things I get to do. I would enjoy it more if I went less often and stayed for more time– basically like vacation travel. I think other fellow travelers would agree given the looks on their faces as I walk the airplane aisles.