Well, best way to decide - do you want all of the entries to show up on your main page?  If that's the easiest way for you to see everything all in one space, go categories.  Will you be posting a lot in each section?  Then maybe separate blogs would be best.  Or maybe divide it up into your Journal and your Reviews, and put all the reviews in one MT-blog.

Kristine

How does one decide this?

I am going to have my main blog (journal type), photos, book, and DVD reviews.  Should I create four different blogs for this type of site and link from a main page? This seems the easier of the two ways to do it.