Most lawyers know that the attorney-client privilege is more fragile than the work product doctrine, so that sharing protected communications with non-clients is far more likely to waive the former than the latter.
There may also be a difference in the burden of proof. In Freeport-McMoran Sulphur, LLC v. Mike Mullen Energy Equipment Resource, Inc., No. 03-1496 c/w 03-1664 SECTION: “A” (4), 2004 U.S. Dist. LEXIS 10048 (E.D. La. June 2, 2004), the court addressed both the attorney-client privilege and the work product doctrine. It held that the party asserting the attorney-client privilege had to prove lack of waiver (courts disagree, but this is the majority position). Turning to the work product doctrine, the court held that the party attacking the work product protection had the burden of proving waiver.
The several differences between waiver of the attorney-client privilege and the work product doctrine serve as a useful reminder for lawyers who sometimes lump the two protections together.