With jailbreak utilities like iFile and Safari Download Manager, your iDevice can seem more like an actual computer than a phone or MP3 player. The two apps allow you to manually download files, edit them, and move them around from folder to folder.
However, there hasn't been a convenient way to natively upload files in iOS (that I've known of), until now. Safari Upload Enabler just surfaced in Cydia, and it allows you to upload content from inside Mobile Safari...