My sense is that the only source likely to cause trouble would be IWE, and that there's a combination of implied license by individual contributors and relatively low legal risk, to repost comments by others.
This is one of the reasons I did a "posts by author" correspondence. This could be used to weed out the IWE-authored posts. Essentially, column text, posts by the various columnists, and the forum editor's comments. All else should be largely in the clear.
IANAL, TINLA, YADA.