In searching for an ancestor I googled and found ancestry.com trees. On those trees I found citations to 'World Family Tree Vol. 1, Ed. 1'. Is this a valid secondary source or is this just effectively citing mostly unsourced ancestry.com trees?
Brøderbund Software were early publishers of Family Tree Maker which was sold supported by CDs of public genealogy data. I strongly suspect that you would be citing unsourced trees based on more unsourced trees if you relied on this source.
In any case, unless you have actually seen the source, genealogy good practice would say that you shouldn't cite it at all. "Cite what YOU see": so you could cite the ancestry trees which you have seen (if you judge them worth citing), but not the sources they cite.
The quality of the trees in these archives varies greatly depending on the amount of effort the contributor put into creating the tree. There are source citations in many of them that are accurate while others are full of inaccuracies and propagate well known errors. They are best used as a hint to help you locate valid sources but if you include notes made by the contributor, it is only fair to cite the source for those notes and stories.