I've watched my download statistics closely about a month for Workout Rotation Diary on Android Market.
I've seen a clear pattern telling me that the latest comment has a huge of impact on daily downloads. When the latest comment and rating is positive, the app can do 100-200 downloads a day. With a loud negative comment being the newest (like at the time of writing I have 2 really negative, the latest being: "USELESS!") it's down to 10-50 a day.
My comfort is that it has 2k active installations and 5k downloads, so maybe there are some individuals who find it useful.
... so not going to kill myself quite yet.