I've been using my iPad for two weeks now, and among all the things I love about it, I couldn't help but notice something I wish Apple would have put more effort into: sharing files between apps installed on the iPad.
We all know that you can share files between your computer and the iPad through iTunes, and even if the system is flawed and could be seriously improved, it works if you just want to copy a document into, say, Pages. You take the the .pages file from your Mac, open iTunes and add it to Pages for iPad file sharing menu. If you just want to send a file from your Mac to a specific app, you can use this method. The problem comes when you want to do some serious work on the iPad and make use of all the apps you installed, because there's no easy way to share files across apps that support the same file types. There's no easy way to share a .pages file between Apple's app and Good Reader, not if you consider sending the file to your own email and then open it with Good Reader an "easy way".
Apps are not linked.
Of course the situation is different from what happens on Mac OS X. Once can argue that on Mac OS X as well you can't link apps to support each other, but on the Mac the Finder is the glue. And with the Cocoa APIs, every app can access the various aspects of the Finder thus enabling you open the same files and share the same features in seconds. In the best case, apps like Omnifocus and DEVONthink can share databases with Omniplan and DEVONagent. But the iPad doesn't have the glue, and you know that I'm not against this way of thinking the OS. I definitely believe in what Apple is doing, but the system is far from being considered mature and perfect. We're missing the possibility to split our work between different apps, at least in a way that's comfortable and doesn't involve sending emails or PDF exporting tricks.
Say I'm working on a post in Evernote and I want to quote something from a PDF into Readdle Docs, there's no way I can import it with a few taps into an Evernote's notebook. Same happens when I want to link a mail message to a Things todo item, or if I just want my spreadsheets to be into Air Sharing Pro rather than Numbers. These are all possible scenarios I'm sure many people have stumbled upon up until now.
If the apps are the OS, then they should be able to communicate.
I'm not saying that Apple should develop a Finder for iPhone OS, I'm just prospecting a situation where a user would need to share documents across two or more apps and doesn't want to do some magic to make it happen. It just has to happen. That's why I think Apple should work on a "unique repository" system for apps' files, or just give them access to APIs where they can retrieve a document created in another application, thus giving the user the possibility to choose what to do with that file. Whether this is graphically represented by a standalone application or an invisible system-wide service, it doesn't matter.
But please, just let these apps talk with each other.