While I was tooling around in the engine compartment today, I decided to install valve cover hold-downs. These more evenly distribute force across the lip of the cover, creating a better seal, and reducing oil leaks. Here are further thoughts on the matter.
I considered fabricating my own, but figured I couldn't do it for less than $12, which is how much the kit costs from iPd. (Yes, I have a crush on iPd and their Vintage Catalog.)