Thanks for your reply Rahul. We've previously discussed putting forums in categories, and in fact, we used to have a greater number of forums. However we found that most people just posted their question in the first forum, so this made it more confusing because things ended up in the 'wrong' place. We also had feedback that people might find it difficult to know where to post their question if they don't know Totara that well. I think there are pros and cons to both approaches. As you say, optimal search is important to making this work. 

We're always interested in hearing feedback from the Community though, so I'd be interested to see if anyone else has an opinion on this.