How does the CPU hashing algorithm used in Yacoin differ from scrypt? Alt-coins are now a dime a dozen and with only minor changes to generation rates, difficulty, and algorithms, they all tend to use the SHA-256 (bitcoin) or the scrypt (litecoin/tenebrix)  hashing algorithms for solving blocks.

A friend of mine recently told me about Yacoin and it uses a modified version of scrypt so that mining via GPUs is currently "impossible".

What are the specific differences between the standard litecoin scrypt algorithm and the yacoin algorithm that makes yacoin currently infeasible to mine on GPUs?
The scrypt-jane modification allows the N in scrypt(N,1,1) to change. Litecoin uses scrypt(1024,1,1). GPU miners haven't taken this into account. But now you have the opposite issue. Instead of the GPU miners getting everything, it's the datacenters who have the advantage.