This is getting increasingly tough in our uber-consumer oriented society but we must stay vigilant about this, hence the dire need for organizations around the world doing things like the Center for Media and Democracy did here. In this story Salon hits the target directly on why disclosing pecuniary interests is critical to ensuring that public discourse does not fall to the fate of political representation in a nominally democratic but factually plutocratic society, namely, pay to play.
The concluding sentence says it all:
Certainly corporations have a right to have their voice heard, but that voice should be their own, not that of a phony expert on retainer.* Note that this doesn't in any way mean that getting funding for engaging in research is inherently bad. It means that it is relevant to the conversation because some people find it politically expedient to provide funding in order to obtain specific findings and disseminate those findings as credible on the facts, and as an academic you ought not to want to be associated with that sort of propaganda, so you want to disclose your sources of support. In my view the research question should attract the funding and not the other way around.