Robin Good: Network World has published an interesting and valuable report comparing eight different web-based web conferencing services.
Their selection of conferencing tools to compare includes Adobe Connect, Cisco Webex, Citrix GotoMeeting, InterCall Unifed Meeting (in beta with v5), LogMeIn Join.Me Pro, Microsoft Lync 2013 (in beta, and part of Office 365), Skype Premium (now owned by Microsoft), and Vyew.com Professional.
Full article (requires registration): http://www.networkworld.com/reviews/2012/102212-desktop-videoconferencing-test-263197.html
Testing methodology: http://www.computerworld.com.au/article/439694/how_we_tested_web-based_conferencing_services/?fp=4&fpid=18