Frankly I don't see this happening for a number of reasons.
- My Laptop is offline most of the time. I mostly use it on the train and don't have wireless broadband. In any case I doubt it would work too reliably sitting in aluminum clad train under high voltage cables.
- At home my download limit per month is about 300MB and is about right for my usage. frankly I couldn't afford to access online apps all the time.
- I don't trust the benevolent administrators of huge online file servers to keep my files confidential if it ever comes to the crunch. If large chunks of the worlds data are in one place then it becomes easy for governments to mandate the removal of 'harmful' material.
And in a corporate environment there is another host of problems with thin client, issues of Privacy regulations and Commercial secrets. An interesting fact comes up in this artilce on The Daily WTF. Switching a corporate environment to thin client increases infrastructure costs. Suddenly your junior desktop support staff who know how to run Norton Utilities just don't cut it any more, instead they need more servers and more system administrators.
Personally I like my Desktop applications and I use them all the time. My laptop is set up how I want it and not how Google wants it. Even when I do use my firfox it is usually to read pages I've saved for off line viewing using the scrapbook plug in. And importantly the files that detail how I'll achieve world domination are tucked away in a computer that can't be hacked without physical access (one of these days I must encrypt them).