From several authoritative sources:
From Crane Cams: "To help seal against moisture and to allow easy future removal, apply a small amount of silicone dielectric grease inside the spark plug wire boots."
http://www.cranecams.com/pdf/90001001b.pdf
From Pep Boys: "Before putting the new spark plug wire on put some dialectric grease on the end of each spark plug to prevent corrosion"..."Simply put the new rotor back in and then bolt on the new distributor cap. Put dialectric grease on each terminal of the distributor cap and replace the spark plug wires."
http://www.pepboys.com/learning_center/car_care/articles/svc_ignition.html
"Step 14: Install the distributor cap." (When retrofitting a Mallory electronic ignition module to an old distributor, it doesn't mention applying grease to the cap internals or rotor.)
http://www.centuryperformance.com/mallory/techfiles/MA0838B_UniliteConv_PN501.pdf
For the Taylor Vertex Magneto (distributor): "9. Lubricate center rotor electrode with one drop of light grease and graphite mixture periodically."
http://www.taylorvertex.com/Magneto_Instructions.pdf
MY CONCLUSIONS, PER THE ABOVE:
1. "Silicone grease" and "dielectric grease" are one-and-the-same.
2. Lightly grease inside the spark plug wire boots and inside the distributor cap connector cups (the outside of the cap) to reduce corrosion and allow easy removal of spark plug wires at both ends.
3. Lightly grease each spark plug tip.
4. Placing a dab of grease on the rotor's center electrode (but NOT its tip) MAY be appropriate since this is a contact-wear point.
5. NONE of these firms mentions placing grease on the rotor tip, nor on the corresponding cap electrodes inside the cap. I suspect these are meant to be grease-free air gaps.
[ June 24, 2004, 06:04 PM: Message edited by: TC ]