Here's an example of a site that posts trumpet tab:
http://horntabs.net/
Pretty much what Chris stated, if you don't already know how the tune sounds, tab is useless.
Guitar players use tab quite a bit. I've met pro's who will even use it to remind them of the best fingering to use in difficult passages (same as trumpet & piano players writing in fingering above a note). String tablature actually pre-dates our present notation system.
The main thing tab generally lacks is duration (rhythm) hence the need to know the tune.
When students and parents at school are looking for a guitar teacher, there are a few I recommend over others since some in our area only teach tab. I of course would rather have the student be able to play guitar by reading the notes instead of just knowing how to put the right finger on the right string!