Desktops aren't going anywhere until laptops catch up to desktop performance on video games and graphics in general. The only reason I have a desktop is for gaming. I imagine most people who buy new desktops now only get them for gaming. I mean honestly, who would choose a desktop over a laptop for anything unless they need to interact with graphics heavily. I suppose you can get a more powerful desktop for cheaper than an equivalent laptop but I think this is a minority case.
(Just my thoughts, no data whatsoever to back this up).
I would choose the desktop anytime. It's just a matter of use case, but a desktop plus a netbook will likely be around the same order of prices as a laptop alone.
True but then you have to sync data between the two devices. Although this might change in the future, there is currently probably not a hassle-free way to sync all of one's persistent data without an expensive mobile data plan for the netbook.
My laptop works fine for gaming. It helps to get enjoyment from quality gameplay instead of bragging about how many frames per second your system can render at the highest possible resolution and graphics settings.
(Just my thoughts, no data whatsoever to back this up).