Remote presentation tool: Dimdim - the best one around?

I need to host an international web-based PowerPoint presentation and I searched around to find Dimdim. 

• It's free for meetings up to 20 people. 
• Neither the host, nor the participant needs to install any software on his/her computer. 
• And it's open source.

Sounds great. Does anyone have experience with this tool, or alternatives? In any case I will report back.