Paillier Cryptosystem - Practical applications?
Yes, for example CryptDB uses the Paillier cryptosystem to implement homomorphic encryption for columns that require it. See CryptDB: Protecting Confidentiality with
Encrypted Query Processing (pdf) for a description.

Whether you consider that use "effective" is another matter. Earlier this month there was a back and forth between the CryptDB developers and some Microsoft researchers who claimed to have several attacks on CryptDB. However, as far as I can tell they were on the other forms of encryption CryptDB uses.