A general remark is the speed of the site. There are many ways to boost this, but a simple trick that I believe efficient is to reduce the number of posts per page. When I participate in a discussion, I only read from where I last posted or read, and generally a whole page contains 2 or 3 times as many posts. It's not that bad having to click 'next' again, if that speeds up the site.
A second suggestion, which I think I posted a year or 2 ago, is a 'print' feature. When I find a very long topic/discussion interesting enough to take half an hour time to read, I like to print it out (dun worry, it's recycled or used paper with a clean side on it). Also, people summarizing/synthesing topics may find a 'lighter' template easier to read. To support printing, you don't need to implement much, just a 'print'-link on the "viewtopic" page which brings you a new, printer-friendly view of the same topic.
PHPBB2 allows to implement this very easily (and i think PHPBB3 will as well). Just copy the 'viewtopic.php' (add the necessary header/footer includes) and make it use the template 'printtopic'. Then just make a new template file for it and you're set.
I did this myself, a while back. It took me one day, including the installing, testing and making the template. If you want, I'll make it for you guys

I love me a bowl of numbers to crunch for breakfast. If you need anything theoryhammered, I gladly take requests.
Furnace of Arcana, a warhammer blog with delusional grandeur.
"I move unseen. I hide in light and shadow. I move faster than a bird. No plate of armour ever stopped me. I strike recruits and veterans with equal ease. And all shiver at my coldest of whispers."
- The stiff breeze