I agree that it is important to avoid having to re-scan a recent topic, to hunt down what we have not already read.
I agree with Marc to see a “chronological list of Most Recent Posts”.
I recommend preventing recent postings to be inserted between older ones inside a displayed topic (the cons outweigh the pros). Other forums I use (like the international Paragliding Forum), only have postings in chronological order within a topic, and then it becomes possible to have a list of links to the oldest unread posting within a topic and read the newer unread ones that follow.
Thanks for your good work David.