Having done lots of videoconferencing over the last 10 years I'm pretty confident in saying that it won't be a satisfactory substitute for face-to-face meetings. Actually, I don't think it will replace much travel at all. Its biggest drawback is that it doesn't scale beyond small groups-- like four people.
Still, this article @work: WORKPLACE TREND OF THE FUTURE IV: Teleconferencing, The End Of Business Travel is a good read:
With drastic increases in airfares, delays and headaches at the airport, along with pressure to become more environmentally responsible, American corporations may eventually eliminate the need for business travel in favor of teleconferencing.
What I do think has the potential to drastically cut back on travel are meetings in virtual worlds like Second Life. I've done plenty of both types of meetings, virtual worlds and videoconferencing. Give me Second Life any day.
If the people attending a Second Life meeting know what they're doing, meaning they can use their client and drive their avatar, then there is nothing quite like a Second Life meeting. It flat works, and is that much better than any other technology currently available.