The talent Improved Sap in the Subtlety tree either doesn't work, is displaying an incorrect tooltip, or I'm very unlucky. The skill gives your Sap ability a 90% chance to stay in Stealth when you use it. I've tried it against 25 mobs now (yes I kept count) and it hasn't worked once. As soon as I enter combat I'm knocked out of stealth, even if I don't get hit.
This talent is very useful for Crowd Control and is probably the only useful CC a Rogue can bring to the table since we don't get Blind, Cheapshot, or Kidneyshot on this server.