If you have the Throw Anything feat, is there any reason to take shuriken proficiency? Are you effectively proficient with all thrown weapons upon taking this feat?
Throw anything in Pathfinder reads:
Benefit: You do not suffer any penalties for using an improvised ranged weapon. You receive a +1 circumstance bonus on attack rolls made with thrown splash weapons.
Normal: You take a –4 penalty on attack rolls made with an improvised weapon.
So, a character with this feat can throw improvised weapons (things that are not intended as weapons) e.g. a purse, a rock, a stuffed moose head, a water melon and so on, without taking -4 on attack rolls.
This feat does not bestow upon a character the proficiency to throw actual weapons (ranged or melee), e.g. a shuriken, a javelin, a longsword, a mace and so on. Thus, a character with the Throw Anything feat will still get the regular -4 non-proficiency penalty when throwing a shuriken. Unless that character has the Exotic Weapon (Shuriken) feat, or is a monk.
As a side note, the only type of character who usually jumps at this feat is the alchemist, because of the +1 bonus to thrown splash. But a barkeeper with this feat and a +2 Seeking Corrosive Moose Head of Returning (corrosive because of the bad breath, you see) would sure be material for a memorable character!
The are rules for throwing melee weapons read as follows:
It is possible to throw a weapon that isn't designed to be thrown (that is, a melee weapon that doesn't have a numeric entry in the Range column on Table: Weapons), and a character who does so takes a –4 penalty on the attack roll. Throwing a light or one-handed weapon is a standard action, while throwing a two-handed weapon is a full-round action. Regardless of the type of weapon, such an attack scores a threat only on a natural 20 and deals double damage on a critical hit. Such a weapon has a range increment of 10 feet.
This is pretty severe, and with the RAW going against, I'd be extremely reluctant to let a medium creature with the Throw Anything feat toss scimitars with the scimitar damage and crit threat and without the -4 non-proficient penalty.
Based on the above, I'd reason as follows: Since Hill Giants, who are both Large and accomplished rock throwers do 1d8 with their rocks, an improvised medium thrown item should do 1d4 points of damage. If the character had the Throw Anything feat, I'd let the -4 penalty go, but still say that throwing a scimitar was a standard action and the crit range was 20x2 (instead of 1d6 and 18-20x2).
Throw Anything has no bearing on proficiency
Instead, Throw Anything lets you do something the rules don't normally let you do - that is, throw objects that don't actually have a range increment, and provides damage for those objects that are not already weapons. Improvised weapons (such as, say, rocks or beer bottles) are still improvised and suffer all the penalties of being such. Non-improvised weapons - such as longswords, shuriken, or scythes - check to see if you're proficient with that weapon and apply any penalties (or lack thereof) as appropriate, which means that if a thrown weapon already has a better range increment Throw Anything doesn't really change the game for you with regards to throwing that weapon.
Without Throw Anything, the rules don't permit a character to throw objects in a damaging fashion unless they're an improvised weapon that would have a range increment (like, for example, a beer bottle or a cooking cleaver). With Throw Anything, you can throw your weapon (or armor, or a dead body, or...) as a weapon with a range increment - but following normal weapon rules in all respects. It adds features to a weapon or object (namely range increment and damage), not to your character (that it, it doesn't change considerations like your proficiency or size).
With the logic of the feat as written, if I throw a shuriken-shaped rock I don't get a penalty, but if I throw a shuriken I do. Likewise, if I throw a long pointy stick, I don't get a penalty, but if I throw a long pointy stick that's been designated as a spear I do.
In my campaigns, I will allow Throw Anything to throw ANYTHING without a penalty for non-proficiency.
There are multiply scenarios available :
1 - Throw a melee weapon that can be thrown. (e.g. spear) or a throwing weapon
2 - Throw a throwing weapon (e.g. shuriken)
3 - Throw an item not intended as a throwing weapon. (e.g. a beer bottle)
4 - Throw a melee weapon that cannot be thrown. (e.g. a longsword)
5 - Throw an improvised item that deals splash damage. (e.g. a cooking pot with boiling soup)
---1 or 2 --------------------------------
-thrown at -4 without weapon profiency and plus BaB+DEX modifier.
-deals the amount of damage as weapon description says plus STR modifier.
-thrown at a range named in weapon description
-critical hit range named in weapon description, otherwise 20 (x2).
-a two-handed weapon requires a full-action to be thrown.
---3 or 4 --------------------------------
weapon profiency is irrelevent, thrown at -4 for improvised weapon (unless throw everything feat), thrown at an additional -2 if not appropriately sized for each size difference. Add BaB+DEX modifier.
-To determine the size category and appropriate damage for an improvised weapon, compare its relative size and damage potential to the weapon list to find a reasonable match. (rocks are said to deal 1d4 damage). add STR modifier.
-10 ft range
-critical hit range is 20 (x2).
-two handed weapons require a full round action to be thrown. (a onehanded weapon that is on size larger is a two handed weapon)
weapon profiency is irrelevent, thrown at -4 for improvised weapon (unless throw everything feat then add +1 instead), Add BaB+DEX modifier.
-Dungeon master determines damage, Do NOT add STR modifier to damage. Splash damage is usually the minimum damage you can roll with the direct hit.
-10 ft range
-Splash weapons cannot crit (though many houserules allow it)(alchemy bombs are exception and can crit for +1d6).
Throw Anything does not grant you proficiency with thrown weapons.
The feat simply removes the -4 penalty for throwing an improvised weapon.
A shuriken is not an improvised weapon.
Think of it this way: without the feat, you can't possibly have proficiency with anything that is not actually a weapon. The penalty for using an improvised weapon is the same as the penalty for using a weapon you aren't proficient with: -4 on the attack roll.
"Throw Anything" is equivalent to the hypothetical feat "Weapon Proficiency (All Improvised Throwing Weapons)"--except that you also get +1 attack bonus with splash weapons.