I have long felt that desktop Linux would become a reality only when you could go to a Linux gathering and find no more than a third of the attendees at the command line. In other words, as long as users are frequently at the command line, the OS is not ready for a big share of the desktop. Desktop users require ease of use.
Earlier this summer, I was at O'Reilly's Ubuntu Live conference in Portland, and the Ubuntu tribe were almost all using the GUI interface. This inflection point confirms for me Ubuntu's claim as the desktop Linux distro. (The conference was especially enjoyable because of the lack of zealotry. It was simply a conclave of the interested with no excess of the us-against-the-world mentality--a factor which made it a far more rewarding experience.)