I literally just finished a quick slide presentation on this very topic that I'm giving to the board of our local United Way - a pro bono client. In the case of United Way, people may know the name, but many cannot articulate what they do - placing unnecessary limitations on its ability to make a difference.
I'm talking to the board tomorrow about three stages of "gettin the word out" if you will, that United Way needs to complete if it ever wants to truly enhance its brand and improve community support.
UW needs to achieve "real" awareness (not just the name recognition kind), communicate relevance (evoke self-interest) and demonstrate impact (prove that its focus really makes a difference in people's lives).
It's probably not a bad approach regardless of what you're trying to sell.
I have I line I use frequently with clients who push me on PR and marcomm when their products aren't ready for primetime:
"The quickest way to kill a bad product is through good marketing."
It generally gets the point across -- or at least gets me off the hook if they insist on going forward with an ill-advised strategy.
Leo ... I think United Way is an excellent example of "I know about it but I'm not interested."
Or, in my experience, it's "I know about it and I resent being strong-armed by my employer to donate." 
In fact, United Way may suffer from "over recognition," in that everyone assumes that everyone else is donating so there's no need for their particular dollars.
Hope your presentation goes well. Keep us posted.
Scott, your line is a good one, and I've used a similar approach before. What do you tell clients who are selling a commodity ... something that lots of other folks do that they feel they do better or cheaper or faster??
Commenting by HaloScan
