The Linux part can not see the hard disk of the machine. I just got the machine yesterday and have not poked around much to know how much it can be hacked. The browser is Firefox, I have not even checked to see if I can install noscript on it.
For most users of netbook, this is a very good deal. When you are in a public wifi in a coffee shop or an airport, you are guaranteed not to pick up a virus. I am not saying Linux is more secure or FireFox is more secure. Simply if you stay within QuickWeb or InstantWeb, there is no way any file can be written to the Windows disk at all!
This is such a big brand differentiation and it can be touted to high degree. But HP for some strange reason is very quiet about this feature in its ads and press releases. From business stand point, every company would strive for brand differentiation so that they dont compete on price alone. Quite strange HP is so silent about it. People are spending on purchase and subscriptions to antivirus software. All that revenue could be targeted by selling a device that is guaranteed not to be infected. Once many users realize that they rarely boot to full windows, they and their circle of friends and family would become more receptive to cheaper plain net access devices in various form factors.
I am very sure Microsoft is giving HP hell for this move behind the scenes. Is it the first sign of PC vendors growing a back bone? Or the lackluster promotion of this feature bodes ill for such an experiment? I wonder.