I think XOR is still at the base of modern symetric (i.e. private key) encryption algorithms. They create a stream which is XORed with the plaintext. The difference between the simple XOR encryption of which you are surely thinking and these better algorithm is that the stream these new algorithms create is not periodic.
If I remember correctly, one end of an HTTPS connection uses public key encryption to distribute a private key to its peer, and then they switch to symetric (private key) encryption. It does this because symetric is faster, and XOR surely plays a part in that.
Feel free to correct me. This subject is far from fresh in my mind.