Would it be possible to analyze somebody's personality and place them on sliding scale based a writing sample? We'd assuming that you have a large sample, like all of the writing that people have posted on forums.
You could look at various factors: the number of positive vs. negative adjectives, the number of exclamation marks, and the average sentence length, for example. You would then tally up these factors, plug it into some sort of formula, and classify the personality of the user.
I think it might be difficult, but it could be cool for a few reasons:
1) A low cost to the consumer, because you utilize data they already have. People could just copy and paste the stuff they've already written from their blog or facebook wall-to-wall conservations, or wherever. At a low cost, they are able to get back highly specific content.
2) Look at how successful horoscopes have been, and they are based on precious little scientific basing. If the data could be put through a few machine learning sessions matching writing samples to results of personality tests, you could at least have some idea of people's personalities. Or, you could maybe put in writing from famous authors and then match people's copy to them. Users would find out that they have personalities more similar to either Gabriel Garcia Marquez, Shakespeare, or Chuck Palahniuk.
3) People could tabulate their results and aggregate them on their blog. Plus, it would scale well if a few algorithms were doing most of the heavy lifting.
Downsides abound as well, but is any one crippling? I see this happening in the next ten years, unless the internet quickly moves out of a text-based environment.