The jail broken iphones have had malware. Yes, they get it because the jail broken ones have a default root password that people do not know to change and they can download anything that they want.
Do you know how much cloud computing you are doing every day by accessing the internet? You do a search. You use databases on computers around the world to search through, you use compute power on Google's network to shift through the results for you.
Again the point of the topic of this thread is that the average PC user would be able to get everything they use their PC for on the internet, using a device like the iPad. This is not everyone, and yes there are lots of issues and concerns with various aspects like data security. A large number of people I know would never miss their PC, and in fact be happier without a maintenance headache.
You mean how much INTERNET computing I do every day? because the internet is a series of networked servers. If I had virtual software stored online then that would be considered cloud computing. I don't.