If you mean filtering the home page activity stream by blog post category, it’s not possible using any of the buit in BuddyPress template tags, functions or queries. I struggled with this same issue for months and finally gave up. If someone can prove me wrong I would love to hear the solution.
If your not using the activity stream on your home page you can just use the WP_Query class to filter the posts.
My use case for filtering the blog posts in the activity stream was to have separate activity stream pages for each post category.
The closest thing I could find was the BuddyPress Links Plugin which creates a links post type that uses categories and is integrated into the BuddyPress activity stream but it required to much customization to get it to work how I wanted.
Boone Gorges’s (BuddyPress Lead Developer) reply to a support
forum topic about using custom post
types with BuddyPress:There isn’t really any support built
into BP for custom pay types, but
supporting them is no different from
supporting other kinds of custom
content in BP. See the BuddyPress
Skeleton Component for some guidance
on integrating custom content into BP
navigation, etc.In the next couple weeks I might whip
up a new plugin to provide a framework
for custom post type support in BP
(front end editing, integration into
nav menus, etc). I’ve had to do stuff
like this for a couple clients in the
past few months and I think I have a
sense of some good strategies.
I also spoke with Boone at length at a WordCamp about adding custom meta or categories to any of the BuddyPress components and using the meta to filter the activity stream. He said it can be done but it would have to be completely coded from scratch and is not something nativly supported by BuddyPress. He also said the best way to accomplish this would be to create a new custom BuddyPress component.