I have a t-hunter and no problem finding treasure spots. Of course this doesn't imply that the system is any good by itself but means that there is a way to use it.
I use the enanched client, i don't know if the integrated map system is the same for the classic one.
The first thing i did was to raise mining to 100. Withouth that i couldn't find water in the sea.
The the "procedure" is very simple: I decode the treasure map, travel near the region where the treasure is, more or less, then i zoom the map until it is at the same scale as the t-map.
At that point I use any recognizable shape in the t-map to determine where is the "exact" location of the pin: when i think i'm more or less on the pin, i simply start digging.
To me the important thing is the scale of the game map: it should match the one in the t-map, otherwise i don't get the sense of location relative to other parts of the environment.
90% of the times i get the chest at the first shot. When i don't i stay where i am and i dig left, right and back. If that doesn't work, i start walking in circle, one step per time, digging in four directions.
Notice that the t-map doesn't contain all the environment detail but you can still recognize in it (and this is useful when there are no enclosed shapes surrounding the spot, like in the middle of a forest or desert) some pattern of colored pixels.
