There was one company that was proposing building an ETT between Chattanooga, TN and Atlanta, GA in the US; reducing the two and a half hour drive to less than twenty minutes. It never really got past the environmental planning phase (plus Chattanooga didn't want Atlanta commuters, because the South and anti-progress).
A successful tube transport system could be technologically ground breaking. Theoretically they'd be faster than airplanes and use a fraction of the fuel/energy (once they're constructed of course; not counting development costs).
But they have all the same design problems of monorails (the worst and least expandable form of public transportation). Difficult to switch lines and difficult to extend. Also you get the additional difficulty of turning, which apparently is very difficult in ETTs.