So on this week's Bombcast Jeff mentions wanting to put up a board to track how many flushes you can get to one 2000 Flushes blue tablet. Back in 2001, my roommate and I did this very thing! Although we just put a pad of post-its and a pen on the toilet tank, and then told all our visitors to be sure to tally any flushes they made.
It was, of course, a horrible way to track it, as the post-its got soggy and old and stained and gross. But we kept at it for what felt like a couple months. When we finally called the experiment (when the water was no longer noticeably blue), we gathered up all the post-it notes and counted up the final total -- 1,300 flushes!
We debated mailing in the post-its to the company and asking for a refund, but let's face it, we were two slackers who'd spent the summer tallying toilet flushes--writing a letter was more than we could manage.