the upgrade.txt that comes with 5.8 mentions the following:
 
4.  Disable contributed modules and switch to a core theme
    (Bluemarine or Garland).
 
I seem to recall I had problems way back around 5.3 doing this. I disabled CCK I think it was and tables such as content_type_XYZ in my db were eliminated, together with the content in them. Am I remembering correctly?
 
So this is keeping me from disabling any contributed modules until I'm sure about this as I don't want to lose data.
 
does this ring a bell with anyone?
 
Neil