I hate when people point that skill out, it has its uses, but it does not seem to work. If I see someone stealth, I put the scan were they should be, and they are not there. And the cooldown on it is 20 seconds while it only lasts for 10 seconds, making an easy window for any intelligent stealther to come in and slaughter me.
When you're waiting for a cooldown on any kind of scanning mechanism your class may have, use an AOE (damage brings them out of stealth). If you're still not picking something up, you're simply checking the wrong spot.
As others have said, stealth is pretty much all these classes have. If you catch them out of stealth, theyre pretty much screwed.
ps: I'm a DPS sorc and DPS merc (not rolled into one...however.......lol)