nitin29:
@dc42: But, isn't Atmega8 at Arduino Uno also natively support USB protocoll? What difference it will make anyhow?
No. The atmega328p in the Uno does serial transmit and receive, and a separate chip converts this into serial-over-USB. The Teensy uses a different AVR chip that has built-in USB support, so there is no need to go via serial. The manufacturer of the Teensy claims "the Teensy has direct 12 MBit/sec USB access" and also claims for the RAWHID library functions "You can send up to 1000 packets per second in each direction", where each packet is 64 bytes (that's equivalent to 640k baud or more).