I have an android phone, but as mentioned in a few posts, there are a LOT of different OS versions for the various Androids. That is a big reason to not do Android at this time.
I am planning to get an Ipad 4 next month. It will be my first I-device. In time it is very likely that I will ditch my android phone and get an I-phone. If I buy an app I can use it on ALL of my I-devices. I often have to buy the android apps separately for each device.
My desktop PC is Windows 7. I do not see myself switching to Mac. I am neutral in the PC vs Mac war. But being able to share files from my PC to my Ipad is a consideration. I am not likely to be alone here. As mentioned a cloud would help, but there are some issues with that. Maybe there could be an export to Ipad option on the desktop.

But it would also need to be reversible from things that happened in game. As Lone Wolf already knows, it would need to be able to be stored locally on the device as well as cloud in case of variations in connectivity.
I am particularly wanting the Ipad version to support Mutants and Masterminds. I own a lot of Pathfinder materials but I like to use them in M&M. I like to get the ability that I want and not have to plot out classes, levels, feats, etc just to potentially be abe to get a given ability that has dubious game balance.
Messing around with the character itself is the main use for me. The in-play is also very useful for a tablet so, like others, I can use it at the gaming table to run my games.
I am willing to help beta test things. Most people on these forums are also likely to be willing to do so.