One of my favorite "little" functions I set the 550 up to do is turn on ext.in for sacd and turn it off for DVD on my Denon AVR for my Philips DVD/SACD player.
I'm sure there are many many things I'll end up teaching it to do.
The only remote I havent been able to setup is the remote for my iMac (to control iTunes).
After reading reviews until 12:00 A.M., I had decided to trade the 550 in on a Home Theater Master MX 700 until I found out you couldnt program it using a Mac. I'll be keeping the Harmony 550.
