1) the decentralized architecture: people won't install servers
2) not concrete enough: they only pile buzzwords and money for now. See also the 37signals criticism http://37signals.com/svn/posts/2330-diasporas-curse
While I mostly agree with (2) I think that we can't criticise (1) based on the current situation on the web because the whole innovation -- if it happens -- is precisely the way all this will be done. Just saying "people having servers? crazy!" is just as pointless as saying "people having personnal computers? crazy" was 3 decades ago ago: people sort of already use servers all the time: DSL boxes and smart phones on the hardware side, bittorrent on the software side. So of course it is not easy, but don't forget that if there is a need for such a thing, it will eventually made easy to use. And concerning diaspora, it's not even about servers, it's about standards: think rather about something like email. The question is rather if will we go towards more decentralisation of the data and more autonomy for the users on the net.