From the meaningless numbers department, drupal.org got its 300,000th issue followup a few days ago.
Nedjo Rogers takes the prize.
No obvious way to know how long it took to reach 100,000, 200,000 and then 300,000. However, it is easy to get from the database, if someone has access and time.
Thanks to: Derek Wright (dww) on the development mailing list.