This is a great feature and it certainly made me read more threads than I usually do, but apparently I seem to have some problems on my both accounts when it comes to adding summaries to the threads. Whether I start a new thread or go back to edit the first post of a thread I had started before, I can't see any field under "Subject" that would allow me to add the summary. I wonder if you could look into it to see what the issue is.
Thank you for doing all this, Tarot!