When used, the Weather-Beaten Journal teaches the player Find Fish, the ability to observe fishing spots on the mini-map in the same manner as the hunter's ability to track beasts. This is the only way to gain the Find Fish ability.
In order to see the Weather-Beaten Journal in the container being looted, the character looting the container must have at least apprentice Fishing training (must have at least 1 skill point in the Fishing skill)
While the Weather-Beaten Journal is Bind on Pickup, the enclosing container does not bind and so therefore the container can be traded/sold just like any other item.
However, if you already have the Find Fish ability you won't see any additional Weather-Beaten Journals; if you open a fished container, any Weather-Beaten Journals will be quietly destroyed before you can see them. The way to check for the item is to mail the container to an alt with some Fishing training and without the Find Fish ability. Then turn off autoloot and check the container. After confirming the existence of a Weather-Beaten Journal, you can safely trade, auction or mail the container.
There have been reports of a peculiar behavior of containers with this item inside: they were apparently empty after looting, but persisted on your bags. This could indicate the presence of one of these journals inside them. Since most of these reports date from patch 2.4 and might have changed since, the safest bet would be to assume the previously explained behavior.
Patch 2.3.0 (2007-11-13): Added.
Patch 2.4.0 (2008-03-25): Now detects Schools of Tastyfish during the weekly Stranglethorn Fishing Extravaganza, as well as Muddy Churning Waters used in the process of summoning Gahz'ranka in Zul'Gurub.