Even though legal professional privilege, duties of confidentiality, and other evidentiary privileges are something I try to keep up with, and though I have just advised a litigation funder on the subject, I would be challenged by an urgent brief to argue the privilege of a communication between in-house counsel and a staff member or officer of his or her corporate employer. There are just so many single-judge cases and so few appellate cases, and I'm not sure they all stitch together too well. The latest is Telstra Corporation Limited v. Minister for Communications, Information Technology and the Arts (No.2) [2007] FCA 1445, and Cutler Hughes & Harris's note on it is here. Telstra's resistance to the other side inspecting certain documents failed for want of evidence as to the independence of the relevant in-house counsel.

The law on the question has recently been summarised in the US in  In re Vioxx Prods. Liab. Litig., 501 F.Supp.2d 789 (E.D. La. 2007). Hogan & Hartson's note on the decision, well worth reading, is here.