After the last upgrade of craftbukkit, worldguard and worldedit - all dev versions, /vanish did not work any more. It says "poff" and accept the command, but you are still visible. I am using worldedit v1145, worldguard vv605, essentials 291, vanishnopacket 3.6.2 and craftbukkit from yesterday dev version

If people see you, then they have the permission node vanish.see. Such as ops.