That is in some cases true Joy, but in 95% of the cases it really has to do with blacklisted serial numbers.
These are some problems that I know of:
1) can't find particular path/file (blacklisted numbers ); call Adobe for a new serial number.
2) error -113: caused by self -extractor. Use Winzip to open update and extract files to any directory and run the update from there.
3) unpacking. It's not advisble to unpack the setup files to the default directory, but create a new directory instead (run the update from there).This solved a lot of the problems for many people. Seems that this temp directory and the PS update don't get along very well.
4) make sure that the main Photoshop file is still called photoshop.exe and not photoshp.exe for example.
5) people who don't read the readme file that is included in the update
