[tkahnoski]

Vague memory from 10+ years ago:

  * Getting real deep with detecting OS/instruction set and edge cases
  * Constantly validating permissions on every directory and file
  * Constantly verifying checksums on everything put in place
  * Concurrency controls to make sure the user didn't launch the installer twice, or the system wasn't live running when being reinstalled.
  * Dependency verification was it's own rats nest of problems
  * Uninstalling

Easier problems:

  * Logging
  * Status tracking (except for really large files things get weird...)
  * Aborting/Cancelling install

[RajT88]

Logging is easier - but deceptively so! Most problems have hidden depth, and logging is certainly a great example.

So - do you want to log variables for debugging purposes once installers get to a certain level of complexity? Great. Now you're logging people's usernames and passwords, and you have to add some functionality to not do that.