Anyone else heard about Gaikai project? Apparently someone is going through the effort to offer people to play full games via browser with no plugins needed. That includes such games as WoW, Eve online, perhaps even Starcraft II in the future. (although, lets face it, any more hardcore gaming will probably be impossible). Anyways check it out for yourself - http://vimeo.com/5404358
They mentioned that its legal as you are actually interacting only via video or something along those lines... anyways they wouldnt invest so much effort into making this happen if they didnt have some legal backing up.
But this should require quite a good internet connection to work nicely right? But we can probably agree that this is a very interesting idea, which seemed impossible 2 years ago.
I think that first person shooters and more serious RTSs will be almost impossible to play at any reasonable level but things like RPGs or MMORPGs should work fairly ok.