Stealth is a very controverial ability, very strong while used and very weak since we cannot use often.
@Sanguinezor: the "pro" reasons you bring are very very feeble. The dps increase provided by shadow focus is neglegible - it's just that there is no better option available. Also, using Vanish as a dps cd (like it was with Overkill) was something Blizzard wanted to avoid, but they didn't get the job correctly since the use of vanish in PvE is tied to a free opener/CP or FW applicationfor Sub.
Obviously Stealth is a clear PvP tool and the advantage to run around unseen is great to setup a strategy. Still, our openers are for control (Garrote and/or CS are way superior than an Ambush) and after that, stealth isn't that useful - Vanish is good for resetting a fight, not for the stealth itself.
A strionger stealth in PvP imho could lead only to imbalances; anyway a bigger use of i in PvE would be cool since there's much more spacing in fight mechanincs without screwing other classes. If we cannot use out control tools and the dps dosen't matter, give us some special tasks to do