Screen sharing with Mikogo

I came across Mikogo in this blog post a few days ago. Here's a review which explains a little more on what it does (actually, there is a Linux version now which I've used).
Essentially it does what TeamViewer does but with the advantage that it only needs to be downloaded (but not really installed -- just extracted) on the Presenter machine.
On the Viewer computers that just wish to join the sessions started by the Presenter, just open a browser, navigate to go.mikogo.com (or join.mikogo.com) and enter the Session ID for the new session as indicated on the Presenter.
I've used Ubuntu, Windows XP and OS X as Presenter and used machines running Ubuntu, Windows 7, OS X and Haiku as Viewers.
I only tried it out on our own LAN but it will obviously work over the Internet, too.
For screensharing and whiteboarding I found it slow so complicated presentations may be troublesome. Not sure what can be done about this but I'll look into it and post if I'm able to find a solution.
Possibly the biggest problem I had was that File Transfer just wouldn't work for me irrespective of what OS I used on the Presenter or what OS I had in the Viewer.
I posted to the Mikogo forum on these problems but have yet to get a solution. Nevertheless, more details are provided in my posts.