Like Netscape back in the mid-nineties, Google is planning to blindside everyone else with an aggressive rush to the cloud and a plan that encompasses everything from applications to transport to radically change how we compute.
Apple, primarily with the iPhone, has redefined what the user interface is, and how software can be reliably delivered, possibly sidestepping the problems PC vendors have traditionally had with third parties screwing up system reliability. This is more of a blend of the Web and traditional client computing but, as you would expect from Apple, a strong step towards better usability.
Microsoft sees the cloud and, I think, recognizes that it needs to make a major step, much like it did for the Internet in the mid-90s. However, it no longer has Bill Gates to drive the change, and Ray Ozzie is no Bill Gates (hell, nobody is Bill Gates but Bill Gates.) Still, this is Microsoft's market to lose and all it has to do is "good enough." However, with a recession looming, what was once "good enough" may no longer be; this recession could be a forcing function driving a substantial change into the market.
Cloud Computing: The Internet Redefined
Cloud computing, along with the massive amount of work going into massively parallel computing, together form the basis for a change that I think will be bigger than the Internet was. They not only redefine where the computing takes place, but open the door to a level of computing power currently outside the reach of the vast majority of people.
This isn't even remotely trivial. Even Google is likely having difficulty figuring out how to make this work before someone else pops up and does to it what it did to Yahoo. Anybody can be displaced; it simply requires some thought on where Google's weakness is and, right now, fortunately for Google, everyone is focused on its strength.
Google can probably be taken out with the right bundle, much like Lotus was in the early 90s. Figuring out what that bundle is, and how to deliver it, won't be trivial, but the "cloud" will clearly be the platform of initial choice because that is where Google lives. (I doubt the "bundle" will be a set of desktop applications either.)
Who Has the Edge?
Microsoft is entrenched, but this actually makes it more difficult for the company to move because the revenue model in this new world will be vastly different from what it was in the old one. Probably more similar to what it currently has for its enterprise agreements or the Zune service than it typically has for packaged software, but making the transition will be a lot more difficult than it was for Netscape, which died in the middle of it.
Apple seems to be sneaking up on this with the iPhone, which continues to look amazingly well thought through, even for a veteran of the phone business, let alone a new entry. But Apple lacks a robust backend and, unlike Microsoft, doesn't really have a subscription anything yet to use as an example of this new revenue system. Even though it has Google's CEO on its board, it doesn't even have an advertising revenue stream of any substantial form (granted Al Gore is on the board as well and it wasn't very green - though that may be changing). It gets the user experience side of this solution better than anyone else, though, so I wouldn't count it out completely.
Google lives in the cloud but doesn't have a real beachfront yet in the enterprise. It's growing at such a high rate that it is increasingly hard for Google to concentrate out more than a few months and remain focused on what is a very fast-moving target. It lacks critical meaningful partners but has purchased a lot of infrastructure that its competitors have yet to figure out. And it seems to have both Microsoft and Yahoo more focused on each other of late, which buys critical time to figure this all out.
If Bill Gates were still in Microsoft, I'd give it the edge because he has demonstrated that he can drive a .NET-like effort. With him out, I think it comes down to Google well matched against Microsoft and Apple as a wild card. If Google can figure out and execute on the right bundle before anyone else, it's a Google market and it will be an upset. If Microsoft figures this out and fixes its pricing model in time (and it gets more of it because it's entrenched), it wins. Apple has to do both well before the other two get their act together, but is actually at less overall risk than either, given that it is also entrenched in the consumer market and has an extremely loyal user base.
One thing is clear, cloud computing will change our world, and it will change it a lot.