Thanks to Doug for introducing me to another neat trick you can accomplish thanks to the magic of Office Open XML (the file format underlying Office 2007) is programmatically adding effects to a Powerpoint presentation.
In a web scenario this could be used to fine tune a customized presentation before delivering it to the end user as a download.
To start with you'd need to create your basic presentation and save it as a .pptx file.
Create a PPTX and save it. In the same way we did for a .docx or a .xlsx in earlier examples rename the file to a .ZIP extension, and drag one of the slides in ppt\slides to the desktop. Edit that XML, and add a transition element as the last child of the <p:sld> element. For example, you might put the following markup between </p:clrMapOvr> and </p:sld> ...
Now you have a transition effect on entering that slide. Try fade instead of newsflash if you'd prefer something more subtle or see a more complex example.