The term “cloud” is used for different sort of things: cloud storage, cloud sync, cloud apps, etc (and then, cloud computing, which is really relevant only to businesses). People like cloud apps like Gmail (your email and your email interface both live on the Internet and are loaded via a web browser each time) because they can access them from anywhere, such as a public terminal. Etc. Sean gives examples where he syncs files between devices.
As Sean writes, the need varies by user. I do all my work on my MacBook Pro.
I cannot stand the Gmail interface, I think web apps objectively :-) suck because they are behind desktop apps by a couple of decades when it comes to interface elements and actions (Gmail added drag and drop about a year ago). When enough features are added to a browser and its JavaScript engine to bring them up to the level of desktops (OS/native-UI), they will be as complex, as hardware dependent, etc, as desktop apps are today.
Dropbox is a shitty service. At least at the time I used the service, they version files and count that against your usage. Their Mac client has many bugs (I sent them in a detailed report including where I think the actual bug might be; no response), in particular one that causes it to lock up the CPU. The idea that I have to move my files into one location (or hack around it with symlinks) is silly.
Practically speaking, syncing is a mess. Duplicate entries in address books. Missed photos in PhotoStream. Endless buffering for MusicMatch’ed songs. On and on.
The whole thing is built on a large set of fragile assumptions (such as ubiquitous broadband access, the point you raise) that crumbles frequently, at least for me. My fix is simple: use a single system for most of my work, lug it around with me wherever I go, back it up to two separate locations.
Doug writes about how nice it is when a contact shows up on another device in a few seconds after you enter it on one. That’s nice indeed. Except when you rely on that, step out of the house with the second device, only to find the sync failed (almost always silently, please note, especially on Apple devices, lest the myth explode :-)) and the information is unavailable.
—ravi