I have 3 PCs running windows. The one I trust the most is running, MSE & Faronics AntiExecutable with Windows FW w/Sphinx software control+router. Also, I'm running Fx with NoScript and Adblock Plus on all 3 PCs. All run in a LUA environment unless I have programs to install or WU.
I use a Linux Live CD for my more sensitive needs and I've experimented with Kevin and Nancy's Operating System (KNOS) which boots from a DVD (in my case) and is also bootable from a flashdrive.
That all being said, I don't use the IPad for sensitive anything since I don't know when and if I might be hit with some form of malware. I have some security sense with my windows PCs. There isn't any security available for the IPad as of yet. If you are willing to learn then most OSs are able to be secured (nothing is 100%). Though, most people prefer to have PCs work out of the box.