ReadWriteWeb has the goods on a new, lightweight, screen sharing web presentation platform called PocketMeeting that looks very reasonable and sounds very good.
While the concept seems very logical, the question of business survivability has to be considered vs. WebEx. The dot.com industry is littered with web conferencing companies that are no longer around. What's amazing is none of the surviving companies ever go out to acquire the user base, which makes me wonder if any of the users are ever paying for the services. Instead I'd look more closely at the company whose technology is behind the service, GeniusRoom. At the heart they seem to have a more robust offering, providing all services in one place, but at a higher price point.
Bottom line. If you're using a free service, you end up getting what you pay for in the end. NOTHING.