A lot of people seem to leave windows on the grounds that it's full of viruses, ending up with OSX or Ubuntu. They rejoice at no longer needing an antivirus, or firewall, and proceed to pay security no attention whatsoever. They're probably better off than they would be using XP without any 3rd party software, but I suspect that OSX + ignoring security is less secure than windows + obsessing about security.
The thing with OSX is that it is very, very, very forgiving of users doing stupid things. You could dig out any 5 year old Mac, not get any software updates or bother enabling the firewall, click every malicious link you could find and throw in a few random apps and 99.99% of the time you'd be fine. And in a way, this is how computers
should work - patches, reboots, av signatures etc. are just boring and tedious to all but a few.
I actually think the world of Windows is a little too much about security
for the average user and I can quite see the attraction of an alternative based on those grounds, the problem is it breeds complacency and in some cases downright ignorance. If you browse some of the Mac forums in the wake of this OSX/OpinionSpy trojan you see comments like "apple will patch this" or "it requires admin credentials to run so this is not a self-replicating virus" - both missing the point in different ways. No more or less ignorant than a lot of Windows users I might add, but how often have we said that the problem usually lies between the chair and the keyboard? And that's platform independent! OSX forgives these people. Windows does not.
Desktop computing appears to be a trade off between ease of use and security. Getting the balance right is difficult, but I do feel Apple are closer to it than Microsoft. No idea where Google will fall on this scale.
If you're talking about ChromeOS on the desktop, I don't know. I'm not even sure it will ever happen, at least in its current form. The current model is "the browser
is the OS" which will work for netbooks but not for anyone wishing to push their PC any further. From what I've read about ChromeOS it looks very secure - the advantage of having a clean slate - but at the cost of reduced functionality (or at least limited to the functions the web can offer you). It wouldn't suprise me if Google's desktop offering was a thin client running ChromeOS. What they will do about more meaty computing needs remains to be seen. An official Google linux distro would have been nice to get away from Windows rather than having a mixed alternative, but maybe the timing isn't right and this is a stop-gap. Google will be considering life after Windows XP like the rest of us so if they were planning on ditching it anyway then no time like the present.