Phew, ok, at least i wasn't the only one suckered into continuing this thread! thought bubble...(hey, wait a minute. if i say that, how do i know he's not gonna come back with a 'got ya' like the rest of these guys? hmmmm....)
Nope, being serious, you probably don't notice it much. If you do it would be in the spring/fall time, and that's also factoring source water, temp, etc, etc.
the only way is to see how long the sample will last for you. so many variables that someone might get way more uses than someone else. I saw a youtube video of this guy that did like 2 swirls of the puck and made enough lather to shave.