That's a terrible example. If this is your primary argument for web services, then they've been obsolete since cron came with UNIX V7 in 1979.
On Mac OS X, without even running the app, iCal has no problem sending me an email to notify me of an upcoming event. How does it accomplish this magical feat? It runs a background process that just happens to have access to my local calendar database, because it's already on my computer.
>The in-the-cloud services which provide the most value to me could not exist without being able to process my data in the background.
And you would have a very difficult time actually using those services without access to a personal computer that already has far more resources at hand to do the same processing itself.