A sleep trap? I know it would be crazy but I am beginning to warm to the the Thief class. Of course as long as I am one not fighting one. 
Theives with....
a sleep trap is not needed... You have something that can put someone to sleep try using it.
Well I know about that, of course! But it would be nice to have a sleeping powder that could affect someone while you where all the way across town!
No sir, I don't like it. Another way for a thief to put you to sleep. DK's have a way, Necro's, Ninja's, Shaman, Thieves - two if this was added, some qclasses, monks under circumstances.
The only good thing is that all of those with the exception of one HAVE to be in the same room with you. With that one exception, you have PLENTY of warning before you fall into a catatonic rest.
haha i dont have plenty of warning, I'm just happily sitting there when all of a sudden
'a sudden pain erupts in your skull'
or
'Someone grabs hold of your neck and puts you to sleep'
he meant you have plenty of warning from the shamans method of putting you to sleep.
One word.
Rangers.
A thief can ruin a melee character's day when he puts him to sleep. If the thief fails, however, he should be in for a world of hurt. A sleep trap would allow the thief to put someone to sleep with practically no risk. That's why I don't like it.