Can somebody tell me for what the private-config.text file is on a 3750 Stack?
private-config.text is used for the switch when it is booted outside of a cluster in standalone mode.
You can configure the name of the private configuration file and tell it to boot from a certain location with the 'boot private-config-file' command. Think of it as a non-changing copy of the config for this switch. If you add the switch to a stack, the config.text gets overwritten by the master of that stack.
"Use the boot private-config-file global configuration command on a standalone switch to specify the filename that Cisco IOS uses to read and write a nonvolatile copy of the private configuration. Use the no form of this command to return to the default setting."