The forum might be big enough now to warrant a few different categories, but I'd hate to see it get too spread out. Jeremiah's suggestions were good, but I think eight categories might be a bit much.
With most forums I visit there seems to be one main category where people post and all others are ignored. Spreading out the categories too much makes it more likely that posts will go unanswered because people only check into their favorite or "normal" place and don't see other posts where their input could be helpful.
One of the things I'd worry about with a "newly diagnosed" forum is that the a lot of helpful advice for new patients comes from people who have been going through this for a while. I'd be afraid that the "old faithfuls" might not be as likely to peruse that category and we'd lose a lot of helpful information. Same goes for chemo - lots of good advice seems to come from people who are not actively getting chemo but have been through it in the past.
If the site does get divided up, my recommendation would be to keep it simple. Maybe a category for personal stories, one for memorials and inspirational stories and a main category for chat.
That's my 2 cents. I like this forum and will support whatever you choose to do with it.