Just did one of those quick and dirty surveys of what staff are using to communicate with range of stakeholders across UK - worth sharing as it probably gives quite a good picture of desktop web conferencing systems being used accross UK Education. Remember focus here is on desk-top systems not Video Conferencing Suites.
Scotlands Colleges have been using http://www.elluminate.com/ for last two years - though they sometimes also use http://www.netviewer.com/
GLOW ( in the area branded GLOW Meeting ) was using the Marratech System and is now going to make use of Adobe Connect http://www.adobe.com/products/adobeconnect.html So most mainstream Scottish Schools will have access to this.
There is also an active community across Education using the hosted Open University Flash Meeting service http://flashmeeting.open.ac.uk/index.html . This is a free service which allows you to set up meetings as well as attend meetings - the Open University offers this service for free to the world wide education community.
It is used to record and broadcast quite a lot of events as well as for hosting meetings.
Finally there is a growth in wholly on-line conferences to get a flavour of these would be well worth signing up for JISC's Innovating e-Learning 2010 Online Conference http://www.jisc.ac.uk/elpconference10