TUAW has an article on why you should disable AutoUpload for iPhoto and Aperature in the photostream of iCloud.
This is what to uncheck in iPhoto, otherwise you will upload all your new photos from iPhoto, which is fine from you iPhone, but if you are shooting camera raw, is going to quickly fill your iCloud (which only comes with 5GB of space) and you iOS device.
I mean luckily I have 25 GB of iCloud space as I was a mobile me subscriber, and I have a lot of documents and comics on my iPad, but it only has 10GB free of the 25GB of iCloud space, so putting up full size RAW images would be disastrous. And you can still add images to your photostream by dragging and dropping, though you can’t remove images (which is plain stupid in my opinion).