Well, they seemed to have learned one lesson from that poster. Unfortunately, it wasn't one about good design or font choices. The current poster extolling us to donate blood uses seven, count them, seven different fonts. One of them is Courier.
Now don't get me wrong. I love me some Courier. It's the hardest working font out there, always trying to make sure you have something on the page when your printer doesn't have that other spifftacular font you chose. Heck, it can even work well as a display face if you know what you're doing. When you don't, though, it ends up just looking sad.
And, sure, you can mix your serif and your sans-serif fonts. It can produce an appealing contrast that draws attention to specific parts of your message. When you use several typefaces of the same sort, however, they really have to have strong contrast if you're going to make it work. And when I say strong contrast, I don't mean "the 'J' is shaped differently," OK?