I use the cyberstats plugin (nowadays my bookmark is set to
here so I can see the shoutbox and the newest posts at the same time). I only click "new posts" when I'm on my phone, and even then it's stupidly fiddly. So I could definitely live with a category system instead of distinct forums and sub-forums; I only use the latter when I'm looking for a specific post and think I can find it faster that way than by searching.