I have not looked into if Samsung is doing anything different, but from what I understand the encryption is software based. That can mean the phone has to work a little harder to encrypt/decrypt the device.
The other type is hardware based, for example, the iPhone 3GS and above has a chip that handles the encryption, much like the Seagate Opal drives if you follow that stuff in the PC world. That makes encryption pretty instant and no real impact on the processing of the device. I don't know if Android does that yet.