What people seem to be missing with this focus on the filesystem is the even more daunting idea that after March: Apple Events are over. That means no more controlling iTunes. That means Growl is dead. That means any plugins, addons, or other software that piggybacks on a major application is dead. That means you cannot take a PDF, run it through photoshop or the finder, then print it automatically. That means the death of, pretty much, any type of workflow that uses more than one application.
No more web development software. No more FTP software. No more Parallels or other emulators (because they can't talk to the Finder! The Finder is an application!) When the Finder is sandboxed.... well, it's all over for just about any application.
Sure, you don't have to use the sandbox yet, if your application will be destroyed by it. But Apple's pushing the "Sandboxed app is a secure app. No sandbox, it's vulnerable." And that is true, but that means any application that does anything worth doing (heck, can Word even talk to Excel in a Sandboxed world?) cannot be sandboxed, and is by definition insecure, and thus will suffer.
This is a big freaking deal.
Edit: As an example, after march no longer will applications likely be able to tell Safari to open up a webpage. Like, say, the documentation for the application.
What about database access? Unless you use sqlite, can you actually get any data from a mysql process? Or did Apple just kill any kind of database program that is useful?
There's myriads of things this is going to affect. And I bet people will be shocked at how much functionality is destroyed by this. Now, Apple might figure out another way to preserve AppleEvents, but if they don't... that's a major, MAJOR loss of functionality for the Mac.
