I'm spending the morning as part of the committee for a thesis defense over in Europe. I'm watching the talk over Skype; we're using a conference call for sound (and as a backup); I have copies of the slides on my laptop.
Is it the same as being there? No. But it's probably 90+% as good in terms of the experience of listening to the defense. It saves me a full day of plane travel (never mind other time overhead), it saves the institution multiple thousands of dollars in air fare and other travel expenses, and if you happen to feel that flying has negative externalities due to greenhouse gas emissions, then it's good for other reasons as well.
If the timing had worked out better, I might have made the trip, and arranged to give some talks to amortize the "travel cost" over more than the defense. But I'm glad to avoid the travel -- thank goodness for modern technology. And as much as I enjoyed the NSDI PC meeting Monday, if it hadn't been down the block at MIT, I would have enjoyed it much less. (Indeed, the location of the meeting was one of the incentives to accept the PC invitation.) I'm still waiting for the tech to get good enough so we can have an online PC meeting (w/video, sound, etc. to mimic the face-to-face discussions of a face-to-face meeting) that we don't have to travel to.