Protoss scouts really suck. The only reason to ever get them is for use against battlecruisers, guardians, and carriers. Mutalisks have a bouncing attack and can do a total of 13 damage per attack (16 with one attack upgrade, +1 at each bounce), while the scouts only do 12 against the mutalisks. (24 against large units, but since attacking mutalisks it's divided by 2 because of explosive attack.) Terran wraiths get to cloak. The best way to play protoss on an island map is to get photon cannons quickly, to defend from early mutalisk or wraith attacks, while you upgrade to get templars, archons, and reavers. Observers are also very nice to have. Shuttle upgrade is imperative, or you wouldn't be able to expand seeing that you have nothing to defend your shuttles with. Defend your base with archons and psi storm. When you expand, place an archon and a templar with psi-storm ability on the upgraded shuttle (with two probes) to kill any air units that the enemy uses to keep you from expanding. It helps to put photon cannons at your expansions, too. Drop reavers and archons or templars as often as possible in enemy bases.