The overwhelming majority of webinar presentations are still made with PowerPoint slides. Each web conferencing technology vendor has a different approach to the way in which they support presentation and display of PowerPoint slides within a meeting.
Some vendors support animations embedded on slides. Some support transition effects between slides. Some support embedded audio/video files placed as objects on slides. Some convert slides to a succession of static graphic images, losing all animations and transitions. Some convert the presentation to a different format (a proprietary internal format such as WebEx's UCF or an open standard such as an Adobe Flash file). Some tell you to share PowerPoints by running a screen share of the PowerPoint running on your desktop. And Live Conference PRO is the only vendor I know that opens the PowerPoint application locally on attendees' own desktops to view the presentation.
I thought I would put together a few comments and opinions about the different approaches for your use when considering selection of a vendor:
1) Watch out for vendors who require you to send your file to them for "back room" conversion to a proprietary format. You can't control how long the turnaround time might be and you lose the ability to do last-second changes to a presentation shortly before event time. Think that's a silly consideration? It happens all the time. One of your speakers gets replaced by someone else and you want to change a title slide. You notice a typo in a product name. Etc, etc.
2) Watch out for vendors who handle PowerPoint display by telling you to open a screen share of the PowerPoint running on your desktop. Screen sharing (aka: application sharing, desktop sharing) uses up a lot of bandwidth, suffers when attendees have slow connections, and is subject to packetizing of information (things move in jerky jumps instead of smooth transitions).
3) I like the vendors that maintain a "nonvolatile" meeting room that can hold a presentation file between meetings. You can upload your file ahead of time and then fire up your meeting in a heartbeat, ready to display your slides without having to do a preparatory upload.
4) If you are really "into" animations and slide transitions in your PowerPoints and having them available in online meetings is important to you, test the heck out of your vendor's support. I have a torture test PowerPoint file that contains some of PowerPoint 2003's most complex animation effects, slide transitions, and color effects. I don't know of a vendor who handles every single aspect perfectly (although some come very close).
PS: Watch out for use of gradient fills, pattern fills, and picture fills inside PowerPoint autoshapes. Gradient fills (this is where a color shades from one hue to another across the shape) often get downconverted to a lower resolution during meeting display, making them look like a grainy, sickly rainbow. It totally kills the nice professional effect you were going for.
PPS: Whether you are a vendor or a consumer, I'm happy to share my torture test file for your use. Just email me and ask for it.
5) If your vendor supports only static image slides, you are almost always better off to do the conversion of an animated PowerPoint file to static mode yourself in PowerPoint before uploading or sharing it. That way you know which overlays are going to appear and in what state, rather than being surprised by the vendor's conversion routine and having to adjust afterwards by trial and error.
Finally, always remember that the technology and display of the file is secondary to the content and source presentation. A lousy PowerPoint doesn't get any better when you show it on a webcast!