I previously covered the decision in Costco Wholesale Corp. v. Superior Court (2008) [no longer citeable] in the context of a discussion about PMQ depositions.  While the premise of that post remains valid, the use of Costco as an example does not.  The Supreme Court has granted review of that decision (denying a Petition that sought to reverse an order compelling production of parts of an opinion letter from counsel to a client):

Petition for review after the Court of Appeal denied a petition for peremptory writ of mandate. This case presents the following issues: (1) Does the attorney-client privilege (Evid. Code, section 954) protect factual statements that outside counsel conveys to corporate counsel in a legal opinion letter? (2) Does Evidence Code section 915 prohibit a trial court from conducting an in camera review of a legal opinion letter to determine whether the attorney-client privilege protects facts stated in the letter?

It doesn't look all that promising for the Court of Appeal's opinion, considering the history of the matter:  a Petition was filed, an OSC issued, the OSC was dismissed without an opinion, the Supreme Court directed the Court of Appeal to issue an OSC, the matter was heard, and, finally, the Petition was denied.  It looks like the Supreme Court is very interested in the outcome here.

[Via Wage Law]