Anyone know what they're used for and how many are needed?

I'm pretty sure they're just for keeping score.
as far as i can tell they dont give any bonuses, though i could be mistaken.

I know that you need to have roughly 3600 at the end of the game to unlock the video player thing.

I'm not entirely sure what else its for.

as far as i've gotten, you use them to unlock an artwork viewer, bgm player, character bios plus a couple of things else that i cant remember / havent gotten yet

Oh. I thought we would come across a shop where we could use the piccarats to buy inn stuff or hint coins. Argh.

I've finnished the game but still answering puzzles and they are used to unlock a music file, a voice file and a film file.

quote Aramis

Anyone know what they're used for and how many are needed?

i did all puzzles and i got 4913 of 5312(us) or 5302(uk) picarats(did a few wrong) and i used 176 hintcoins of 200

u need 100,000 picarats because when u complete the game u need to do 50 puzzles and the ladie which lives in the big house has another baby and she wants to sell her house but nobody has enough money so u have to go up to her and she say would u like my house u have to do this extremley hard puzzle if u get it right u pay her 100,000 picarats and u get the house .

picarets are used if you need a hint to help solve a puzzle, there are not many in the game, each puzzle gives you three hints, each hint costs you one picaret, make sure you tap on eveything to get them, i.e, rooftops, barrels, chimmenys exc. hope this helps.

puzzled as well is confusing picarats with hint coins

For accurate information, check out this FAQ ("What are the picarats for?") ... although this has already been largely answered in this February thread
http://professorlaytonwalkthrough.blogspot.com/2009/05/faq.html