I kept the first one I got on day one (12/6) (related to this: »
Typo in theme's code ). I kept the second I received 10 days later (when I went from level 0 to level 1--"thanks for visiting regularly..."), and I think--not completely sure--I also kept the one from somewhere around going to level 2 ("give us a review..."). I had 6 (plus or minus 1) system messages before today.