Internally they all work the same - Devices and Activities. Activities automatically takes care of turning things off and on and selecting inputs. You can map any command from any device to any regular button (LCD buttons or hard buttons excluding the special buttons like Activities, Devices, Media, Sound, Picture, etc.).
What you can't do:
Directly control the startup order of devices. You can indirectly control it through power on delay settings or support can fix it for you.
Customize the OFF button. OFF simply exits the current activity without starting a new one which results in all devices being turned off (if the harmony turned it on).
Do unlimited user macros. A limited version of this is returning shortly with the ability to send multiple commands to different devices with one button press. If it also allows you to send multiple commands to the same device then this will work for most macro situations (it's limited to 5 commands but you can group commands together by learning them in RAW mode first, so theoretically you could get up to 15 or so commands). The good news is most people don't need any macros and this new feature should work for most of the rest.
You can use activity startup and stop commands to do certain actions: you could have two watch TV activities - one regular and one CC - such that the CC activity turns on CC and mutes the receiver upon startup and turns off CC and unmutes the activity upon exit. Then you can just switch between activities to turn CC on and off.
