I envision a software service, running out of sight on the target computer. There are user/vendor supplied plugins that provide interaction with different sites, like LJ, YouTube, etc. A simple config tool would let me set it up on my computer, configuring the loaded plugins, and which directories they monitor. An advanced config mode would allow the user to tweak polling intervals, etc. When a new file is created in a monitored directory, the appropriate plugin gets the file and is told to do whatever it does with that kind of file.
An LJ plugin, for example, would convert any text document to HTML (RTF, Word, etc. would be "formatters" that are part of the environment) and upload the file as a post via one of LJ's programmatic interfaces. LJ returns a post-id, and the plugin moves the posted file to a sub-directory with the post-id assigned. The plugin also notes the creation date. To delete the post, I delete the file. To edit the post, I edit the file.
Here's the real beauty of it though- using tools like FUSE, they wouldn't even have to be real files. You wouldn't be storing a zillion files on your system, one for every LJ post. But it would look that way, and feel that way.
This same idea, applied to email, seems like a dramatic change in the way of doing business. I think it'd be a good change. We're so used to email clients that I don't know if there'd be any adoption, but I know having an inbox that can be mounted as a filesystem, with every email as a file would streamline lots of my work. Sure, the actual messages are stored in GMail, but I can have scripts that run locally on my machine to clean it up.
Seems cool to me, anyway.