When users create a fresh new MySite in SharePoint MOSS 2007, they do
not see the Content Editor Web Part (plus many others, like Image web
part) under the Miscellaneous web part section specifically, in IE 6/7
or FireFox.

Is this something that must be enabled/activated before site creation
at the site collection level?

On my user account I was able to select the content editor web part,
but after deleting my MySite and re-creating it, it no longer shows up
in the list. Any user creating a new MySite does not have it available
in the selection list.