I'm working on it. Im in the 95 range and I love it, I am more likely to spend my time irritating the people doing a spawn than waiting for the 120s.
As far as using it to steal, its kind of double edged. If your watching a mark do a spawn (say im looking for my 1.0 detect/ninja SoT) and you see him randomly invis. Theres a chance that they got a reward and are trying to hide the item in their pack. You have the ability to reveal them, snoop them, and target it (if you use an item to target), but you have to wait for the timer on the detect to be able to steal it. In that instance you may be ok, to let him go on and take it around the next corner or next time he stops to kills spawn. BUT i've had a couple instances where revealing the mark has tipped him off and he's left the spawn. One of which was a .9 taming, which is now added to the short list of steals i must make before i quit UO. Im gonna start ranting...
ANYWAY... It is useful but you need to be careful when you use it. It is just like revealing yourself if the person is paying attention. And dont use it when you plan on making a steal targeting for the reveal will replace your target for the steal, even if you leave enough time for the skill timer.