I can’t remember which technology columnist predicted on-demand television in 2-3 years, but I do remember thinking it was a seriously optimistic projection. The trouble was in my view of how on-demand TV would work. I saw it as a giant server somewhere. Viewers would use their cable or satellite menu to navigate to the server, select a show, and watch it on their TVs. That’s not how it shook out. Instead, ABC got the ball rolling by putting a few shows (like Desperate Housewives and Lost) on Apple’s iTunes. The success of that experiment opened the floodgates, and it turned out that 2-3 years was too long an estimate, not too short.

Online viewing of TV fare has become so common that Nielsen Media Research will begin measuring it as part of its famous effort to rank the popularity of TV shows. The Wall Street Journal reports that the online measurement effort will roll out over several years and will include not just online viewing, but also shows watched on iPods, cell phones, and other mobile gadgets. The article reports that Nielsen will equip its Nielsen families with devices designed to facilitate the monitoring of the families’ viewing habits.

Convergence, it seems, has arrived.