While I'm sitting here still waiting for iOS 4.2 to be released, I'm continuing to think about iOS 5 and how I'd like and iPhone and iPad Files app, similar to the existing Photos app but serving as a repository for documents and other non-image files. It's something I asked for back before iOS 4 was released and is something I want even more now. I don't need or particularly want full access to the iOS file system (and there's a Jailbreak for that if I do) but Iwould like an official and officially supported place where my files are surfaced and a common way to get to them from within any app.
For example, If I get an email with a document attached I should be able to tap and hold, get a popup, and Save to Files the same way I can save pictures to Photos today. Everything from Apple's iWork suite to Documents to Go or QuickOffice, to GoodReader or Readdle Docs and all the others should be able to bring up a file picker as easily as they bring up an image picker today, and I should be able to open and save back as easily as I do photos in any of the numerous image editors today.
Apple already provides something vaguely similar to this... for iDisk files. They released it back in July, 2009. Now the cloud is nice, the cloud is fine, and the cloud may well be the future of file storage, but until that future arrives there needs to be good local access as well. And there needs to be a seamless way to round-trip the files between apps. (Which certainly isn't the case even with iDisk and especially not with Apple's own iWork suite.)
(The ability to move Files -- and Photos -- into and between folders would great as well).
With Retina Display it's easier than ever to work on iPhone and iPod touch documents, and with the advent of iPad and its big screen, it's realistic to do far more file work on the go.
A useable Files.app would make that a reality.
UPDATE: To expand a little based on the comments below, being able to access what's stored in Files.app (and Photos.app) for that matter not just via any app but via Safari as well would be huge. It would eliminate one of the reasons it's so inconvenient not having a Facebook for iPad app by way of just one example.
A cloud connection to both Files.app and Photos.app is also the way to go, so it's easier to move and sync (i.e. backup) files and photos outside just the local device. That's why iDisk (and apps like Box.net and DropBox) only solve half the problem, and MobileMe only syncs part of the data I want synced.
Keep the ideas coming!