When I first used an iPod (after trying several other MP3 players), I said "Wow, someone finally got it right." When I first used an iPhone (after several years with a Treo), I said "Wow! This is incredible." When I first used an iPad (albeit far too briefly!) I said "Wow, this is fantastic."
My experience with MobileMe has led me to exclaim many times using a variety of words, but none of them are suitable for publication here. Do you know anyone who uses MobileMe and says "Wow, this is great!"? I don't. I know a whole lot of people who use MobileMe who say "Well, it works OK most of the time" or "I haven't had to 'nuke' everything and start all over again in a few months." In particular, iDisk is an embarrassment compared to something like Dropbox in terms of seamlessness and reliability.
Then there's the issue of storage space. If you pay for MobileMe you get 20GB of space for $100/year. If the Finder is going to die, Apple is going to have to make iDisk (or, hopefully, its much-better successor) mandatory for all its users. Are users going to foot the bill for this or is Apple going to eat the cost? My iMac has a 500GB drive, only 80GB of which is available. Am I going to have to dump a lot of content or is Apple going to host it all in the cloud? And before you say "streaming" let me suggest that it will be a cold day in Hell before people are willing to give up locally stored music for 100% streaming. Also, who is going to pay for the storage and streaming costs?
The cloud will not save us.
The idea of abstracting the file system from users may sound appealing to some. As Sachin mentions, this is how iPhone OS devices work right now, "Each application has its own sandbox of files and data." Which is great until you need to do something with that file. Having used both iWork.com and Google Documents, I don't see them replacing the need to email someone a file, have them make changes, and email it back any time soon.
Of course email has worked like this for a long time. I don't store any email on my computer, it's all in Gmail and I access it from my iPhone or MacBook or iMac or hopefully soon an iPad. But email is the exception. It's easy to get new information into email or out of email. It is also, for the most part, very small amounts of data.
Sachin imagines a world where all of your files exist in separate "packages" (much like the "All Mail" in Gmail) and you just access what you need through the tool that you need. That sounds great, assuming that you've never tried to launch iPhoto and had it fail to show you any pictures, or tried to launch the camera on the iPhone and have it immediately shut down again. Not to mention the fact that storing digital pictures is becoming a huge storage issue as well. Is Apple going to store all of my RAW images in the cloud too?
Predicting evolution is a difficult thing. I remember reading once that there was someone in the late 1800s (I think) who predicted that in 100 years people would no longer have a "pinky toe" because it served no real purpose.
The lack of a usable filesystem in iPad is already a big issue, perhaps the biggest issue faced by a number of people who are trying to use it for content creation and management. I'd be willing to bet that we will eventually see some sort of a "safe common area" where various applications can read/write to. And after that will come folders, because putting everything in one folder is not viable long-term. Don't believe me? Take all of the files in your Home folder on your Mac and put them on your Desktop without any folders. Or create "Saved Searches" for certain kinds of files, such as PDFs or images, and try using them exclusively for awhile. See for yourself if your exclamations are inspired by awe or anger.
The Desktop/Folders concept may be old, and it may even be outdated, but I think it will be with us at least for several more years. Apple may have killed the floppy drive without mercy, but only because there were other alternatives available which were clearly better such as CD-Rs or even USB drives. These alternatives worked mostly the same way, but had higher capacity and were cheap. Right now hard drives are cheap, with much higher capacities than anything you can easily replicate in "the cloud." I don't think we'll be rolling out a coffin for Finder anytime soon.