One of our customers was having a strange installation problem after upgrading their Mac from 10.4 to 10.5. It turns out they reformatted the drive as a case-sensitive file system. During the installation, a utility gets downloaded from the server. The installation process specifies a pathname to execute that utility, which doesn’t match the case of the actual filename.
We’re in good company, though. A lot of applications including Photoshop CS3 won’t install on a case sensitive volume.