One thing I think people need to bear in mind with stealth mechanics is that there is a tradeoff between complexity, class balance, and plausibility. You can certainly invent situations where the new rules produce ridiculous outcomes, but to me that isn't a serious problem. The real criteria should be how well the rules work in most circumstances, and whether the rules help balance the rogue class. Generally I think the cover or concealment the rogue is using to hide will be pretty large and substantial, especially since everything in pathfinder tends to be at least 5 feet wide (e.g. a large wall section, a large door, very dim light, thick underbrush). The environment will usually provide ample ways to role-play the results of the stealth check in a convincing manner. As for balance, the new rules certainly make it easier to play rogues the way they were intended (the core rulebook talks about rogues sneaking and avoiding head to head combat, doesn't even mention flanking). Stealth is fun and it takes skill to use well. I would much rather rely on these stealth mechanics than the Ninja's "vanishing trick" or invisibility potions.