I buy all my content digitally rather than getting discs so iTunes is a good place for me, my friend acquires his films in a rather more dubious fashion so has installed XBMC on his and it works a treat.
The thing I mainly use it for is streaming music to the good speakers in the house.
When having a party leaving an iPad hooked up to your remote iTunes library is brilliant as people can pick it up and change the house wide music in an instant.
iPad > iTunes Library on computer > All airplay devices in the house > win