Sometimes, the presentation just disappears. The file becomes un-readable or just appears to be gone. Usually this happens at the worst possible time.
Other times, you try to save your presentation and get a message the device is full, even when you think it isn't.
Never try to save the file to anything but the hard drive. If you need to carry the presentation from computer to computer, save it to the hard drive, close PowerPoint then copy the presentation file to the floppy drive, CD, USB drive, network drive, etc.
PowerPoint doesn't work well saving directly to non-permanent drives . It tries to create and use temporary space in the same place as it saves the main file. If working from a diskette, there probably isn't enough room for both the presentation file and the temporary space.
On a network, saving to network drives instead of the local hard drive will create a lot of network traffic as PowerPoint accesses not just the real file, but the temporary files as well. This increases the chances file pieces will get lost. Things get even worse if the network connection goes down while PowerPoint is accessing one of its files on the network drive.
Don't save directly to the CD drive, either. It, too, may cause problems The only time PowerPoint can write directly on the CD drive is when you are running PowerPoint 2003 on a Windows XP system with a CD writer and doing a Package to CD. Even then, just because PowerPoint is able to do it doesn't make it a good thing to do. It's probably wiser to use Package for CD's Copy to Folder on the hard drive and then burn those files to the CD.