The Xobni blog has a practical suggestion on making email easier to manage for your recipients, Re: Fwd: Your Subject Line Stinks - 4 Subject Line Tips
In a world of clogged inboxes and the wide-spread use of portable devices, conciseness and quality content are of the utmost importance when sending email.
An effective subject line is a great place to start.
The four suggestions are (with much more detail in the blog)
Tip 1: Relevance is Key
Tip 2: Make it Searchable
Tip 3: Say it in One Line
Tip 4: Use Acronyms
These are all about making life easier for your recipients. Anything to stop some of those "what's this about" thoughts from revolving through the head of your recipient is a good thing.
I have written about this general idea before (Is email really so evil, I am paid to work, how about you, Yours is bigger than mine, ha ha, amongst others), but the biggest idea along these line: Don't send it, if it doesn't need to be sent.
So, think about how your email affects the people getting it, including providing useful headlines... but don't spend too much time crafting the perfect headline. You don't work at the New York Times.