I am the author of this tutorial. If you are interesting in contributing a section to this tutorial, please get in touch. Some suggested topics: survival analysis, mixture models, classification, time series models... Twitter @markdregan
It would be nice if random variables were denoted by capital letters to distinguish them from particular observations.
In the section about regression you should have the conditional mean of Y equal to \beta X, rather than the overall mean.
Of course, this doesn't really matter too much since the substance of the tutorial is correct. I thought I'd mention it though because sloppy notation can undermine your credibility in some circles, and the equations are the most notable object when you're just skimming the page.
More (very) pedantic notes:
Usually, if you're going to express a sum with \cdots you put A+B+\cdots+Z (with plus signs on both sides of the ellipse for clarity)
The probability operator is usually denoted with a capital P
The log function shouldn't be italicized, you can just type \log to avoid this
Distribution names in statements like y~Pois(\mu) aren't usually italicized.