Because I like to break the everliving fuck out of things like this, I put in a ridiculous amount of my posts to see how it would stand up under thorough testing.
The results for the bulk of my prose: an overwhelming majority of James Joyce (19 posts) and William Gibson (12 posts), as well as Stephen King when I write lazily or when I'm doing horror (39) and Cory Doctorow (23) when I'm writing casual RP posts or writing in my own voice.
I also got quite a few hits each for Margaret Atwood, Anne Rice, Arthur Clarke, J.D. Salinger, David Foster Wallace, Chuck Palahniuk, J.K. Rowling, H.P. Lovecraft, Ian Fleming, Leo Tolstoy, Kurt Vonnegut, and Vladimir Nabokov. Ian Fleming tended to show up for my action scenes, and Chuck Palahniuk and Tolstoy for my more descriptive posts. Anne Rice tended to come up whenever I wrote anything remotely referring to kissing or sensual stuff, so I'm wondering if that's just a flag they use for comparison. Salinger came up for a lot of my dialogue-heavy posts.
I also noticed that certain characters I wrote ended up consistently in one style. For example, the overall results for my posts from Penumbra (an old horror RP of mine) came up as Stephen King. But my Penumbra character Danielle (one of three characters I used) came up every time as J.K. Rowling. One particular monster from Penumbra read as Vladimir Nabokov. Another character of mine from a fractured fairytale RP, Roland, was always Mario Puzo despite my narrative posts from the same RP coming up as L. Frank Baum. And my posts from the Hitchhiker's Guide roleplay registered as Douglas Adams, so fuck yeah.
Another thing I noticed was that putting in really sparse, lazy posts (what I would consider my worst posts) came up as Dan Brown. (That seems about right.)
Kind of interesting when all's said and done. I'd say that while it did throw random things out there now and then, it did show up broadly as the same four writers across many different genres and RPs and characters. There was also a solid chunk of the same "second-tier" group of writers, what I guess could be attributed as "influences" rather than overall style. So while putting in a handful of posts might not be a good indicator, you can probably trust it to be on to something when you get upwards of ten hits for the same author.
Now, if you'll excuse me, I'm going to go write the next Ulysses/Neuromancer/Salem's Lot/whatever the fuck it is Doctorow has written. :U
EDIT: I tried putting in THIS POST, and got James Joyce again.