This is one I created for the blog blog.poltrack.net. They are created by linking the frequency of words in a document to the font size, boldness and sometimes color of the words. Obviously SNOW has been a prominent noun in my blog.
You can create your your own from the website wordle.net.
You can create one from pasted text, or any website that has a RSS feed (try musings.poltrack.net).
I recommend you read the FAQ on this website, it's very entertaining especially the question about the "Sexsmith" font.
This cloud tells a bit about my use of words, but has no information about their importance to my readers. I get a vague idea if I get a comment or a +1 check mark, some analytic data about page hits and time on page but it is a hit or miss exercise.
Google+ recently added a new feature called Ripples showing how public posts are shared (on Google+). Presumably if your post is interesting and compelling it will be re-shared. For example the Dalai Lama: