As we all know, Microsoft stops developing security patches for Windows XP very soon. If a bug in the kernel was to be found that would allow an attacker to take control by, say, sending a specially crafted UDP packet, this would not be patched.
But what if the system is a desktop behind a common NAT router and the only internet application is a browser? Exploiting any bugs will have to happen exclusively through the browser. By running the latest version of Firefox or Chrome, wouldn't the system be reasonably secure?
Of course no suspicious attachments should be opened, but that is the case with any system. Perhaps in XP you can ruin the entire system with a virus whereas on a 7 machine you can only mess with the user's account, but userspace contains enough juicy stuff that I wouldn't say this makes much of a difference on a single user system.
For now I see no immediate risk in running XP for another few months on a desktop when Google Chrome is the only internet connected application. It saves someone buying a new computer. I have already advised the owner not to do online banking on it (better do that on the newly bought work laptop), but besides that...
Did I miss anything obvious in my reasoning, or is XP secure enough for casual use in this case?