If you have problems starting up your photoshop version 6.0 and later (cs3 is version 10.0 btw) and photoshop start hanging on at the splash screen at “Reading preferences” then your custom preferences for photoshop is corrupt or deleted in a mysterious way. To fix that you can easily delete your custom preferences and let photoshop use the default preference.

Example:

1. Press and hold Alt + Ctrl + Shift while starting up photoshop. A popup window will come. (Mac: Command, Option, Shift)
2. You can also simply search your hard drive for a *.psp file and delete it. Somethinglike “Adobe Photoshop X Prefs.psp”.
3. Under Win 2k/XP the preference file will be found at:
   %windir%\Documents and Settings\~username\Application Data\Adobe\Photoshop\[version #]\Adobe Photoshop [version #] Settings

[NOTE: You need to set Window's Explorer Options to "View Hidden Files and Folders" to display the Preference file]

Source: adobeforums