Increase revenue and efficiency. Decrease cost, server load, and monthly bandwidth
One simple number to change will increase your revenue on your Google adsense ads. And that's default thread length.
Currently every page in a thread contains 25 posts. Decreasing this to something less arbitrary such as 10 or 15 would do wonders for BF. 15 seems to be a pretty common number amongst high traffic forums.
Decreasing this number will decrease the amount of data per page load. Reduce SQL stress since less posts per thread page are being loaded, less images in image centered threads being loaded.
Users who are searching the forum are likely only after one post in the whole thread. Users who are returning to a thread are usually only interested in the last handful of posts. People who want to read a whole thread front to back will load more pages, which is actually beneficial.
More page loads = more ad views. Also, when thread pages are narrowed down to 10-15 posts, the topic is generally more centered, making your context based ads (adsense) more targeted which obviously increases CTR.
Just my 2 cents which will earn you lots more then 2 cents.