Comment 2 for bug 173954

"Guided - use entire disk" means "erase entire disk". I'm nearly certain that a warning message would have been displayed at the final step (the one where Next changed to Install) saying that the following changes would be written to the disk, including the text:

 WARNING: This will destroy all data on any partitions you have
 removed as well as on the partitions that are going to be formatted.

I suspect the real issue here is that "Guided - use entire disk" doesn't adequately describe what's going to be done. This was identified as a high-priority usability issue at our last development summit, and we will be rephrasing this for 8.04.