I think we need to be very clear in a lot of different places that PR
firms editing Wikipedia is something that we frown upon very very
strongly. The appearance of impropriety is so great that we should make
it very very strongly clear to these firms that we do not approve of
what they would like to do.
It is all well and good to say, well, it is ok so long as they remain
neutral, but if they really want to write neutral articles, they can do
so, on their own websites, and release the work under the FDL, and
notify Wikipedians who are totally independent.
Additionally, it is always appropriate to interact on the talk pages of
articles. If a PR firm is not happy about how something is presented
about their client, they can identify themselves openly on the talk
page, and present well-reasoned arguments and additional information and
links.
Of course it is always going to be the case that unethical practitioners
may get involved in inappropriate behavior, but I think this is no
argument for simply accepting it. Rather, it is a strong argument for
asking people to do this the right way: transparently and allowing
independent editors to make the actual editing decisions.
--Jimbo