Have it ever happen to you? You just imported some files to iPhoto, and iCloud Photostream start to sync. You then realize you are on 3G data, and do not want your Mac and iPhoto's PhotoStream to eat all your available bandwidth.
Well, here is a way to stop PhotoStream uploading the pictures, until you are connected to your ADSL .
First turn iPhoto off, then, open the terminal and type:
ps auxw | grep iPhoto
You will see something like this:
user 276 0.9 0.4 2519652 16872 ?? S 27May12 1:13.45 /Applications/iPhoto.app/Contents/Library/LoginItems/PhotoStreamAgent.app/Contents/MacOS/PhotoStreamAgent
In this case the first number is 276, yours will be different almost for sure. Anyway, write that number down, and run this command.
Use your number instead of 276, that will stop iPhoto, until you open it again, then it will continue where it was.