Cool idea. Anyway, I created a Top Stories Directory 2 days ago too. It will record down every number one stories starting from 2 days ago. But, it lost tracking some stories due to some bugs. But, I already fixed them all.
I scrape only the front page once every ~4hrs (minimum)
Nearlyfreespeech.net doesn't have cron yet, so I'm using onlinecronjobs.com. If you want to scrape it on demand just go to http://hnweekly.watdahel.com/index/scrape
It's not 100% accurate, but it's close. The reason I did the website is so I can catch up with the good stories that were submitted earlier during the week (I usually read during weekends).
http://hn.siong1987.com