There are two kinds of blurb that authors need to produce, and they are subtly different.
The thread refers specifically to hooking the publisher, which is the first and probably the most important thing we need to do. Hard to improve on Wolfe's advice for this. What they're looking for is the ultimate synopsis - a beginning, a middle and an end, in maybe 150 words. They need an overview of the finished product. They don't want catchy or clever, but they do want a fair representation of how you write.
If your pitch is successful, the second kind of blurb you'll be asked for is for the jacket, to be read by potential purchasers. This time you don't want to tell the whole story, however briefly. You want to introduce your main characters, in just enough words that PPs might start caring what happens to them, and sketch in the difficulties they face (if no difficulties, no book!) but stop short of the spoiler than might make a PP think, "Well, now I know what happens I don't need to buy it!" Some sort of a cliff-hanger, as long as it isn't too crude, can work well, completing the blurb but leaving the PP wanting more.
Writing a good blurb is harder than it sounds. The fewer words you have to play with - the publisher will specify what he wants for the jacket - the harder it is. I always find I've grossly over-written, but the exercise of cropping is beneficial in its own right: makes me concentrate on what really matters.
