I was about to ask whether it would be difficult to include something like /r/all (i.e. the ability to view posts from all subreddits without having to visit each individually), when I tried just editing the url to http://lesswrong.com/r/all, and sure enough, it works (it shows posts from both Main and Discussion)!

Is this functionality documented anywhere? Also, is it possible to view just the post titles on /r/all, without the full text?

Edit: Yes, it is possible to view just post titles: http://lesswrong.com/r/all/recentposts/