A big challenge any remote presenter faces is that it's too darned easy for an audience participant to tune out. You're already sitting in front of your computer, watching a demo, and then an important email shows up. Or an IM pops in. Or someone drops by your cube and wants to chat. So you start typing, or chatting, and if you haven't muted your phone line, that background noise is going to come through.
This is frustrating for the person presenting. Imagine if this scenario played out in a conference room. There, the presenter would politely ask to table the side discussion to later, or see if it was something he could help with. If it wasn't related to the item being presented, the people could step out of the room and not distract anyone. But when you're demoing remotely, this isn't an option. In that situation, you need to be able to mute the person remotely. If you can't, you're never going to get your message across.
Case in point:
A few months back, I attended a webinar that Microsoft was putting on about Visual Studio 2010. The presenter had to stop several times to ask people to mute their lines. Now here's the thing - if you're the person who's stopped paying attention to the call and is now typing, chatting, or playing video games, you're not going to notice the presenter asking people to mute. So he had to contend with a metric-crap ton of background noise. As an audience member, it was extremely frustrating to try and filter out the noise from the presenter's message, and to be honest, I can't remember much of what he talked about.
When I give remote demos, I have the ability to mute people remotely when stuff like this happens. The program I use (GoToMeeting) also has a chat window. So if there's a lot of background noise coming from a particular participant, I'll say "Ok, folks, it sounds like -insertPersonNameHere- has a really sensitive microphone that's picking up a lot of background noise. I'm going to mute them, but if they have questions, they'll be able to let me know via the chat window, and I'll unmute them."
So make sure you have the ability to mute people remotely. It will only make your presentations run smoother both for yourself, and for your audience.