Expecting users to spend a "couple of days learning the basics" of command lines is a major reason why more people don't use Linux. When I tell people the N900 runs Linux some of them seriously ask if it's only intended for programmers.

Linux will only become mainstream if it doesn't require any command line input from a typical user.

If the GUI is slower than command lines, that does not mean you can expect the user to learn command lines, it means you demand the GUI be improved in whatever way it is deficient. The GUI is the only game in town if you want Linux to be for more than just hobbyists.