@dilettante: Naw, I'm talking about Dropbox specifically, not a generic online filestore/collaboration site like box.com that has you hopping around a semi-stable, pokey, "Web2.0" website to do everything (personally, the more I use them, the more I'm hating web applications).

Dropbox runs a client app that integrates into your shell. It makes a folder in your profile set called "Dropbox". All files are stored locally on your machine. Anything in this Dropbox folder though gets background synchronized to their cloud. I don't have to bring up a web browser for anything. There's no "Web" in Dropbox (which is also why I mentioned it in the non-web post I did. )

If I have Dropbox installed on two computers, then the files in that folder will synchronize behind the scenes automatically. If my house burns down, I can install it on a new computer and those files will download/synchronize to it.

You can also share files using Dropbox, but it requires the other person to have a Dropbox account so you can flag his account as having permissions to see your files or a sub-set of your files. These then would just synchronize in onto his computer as well in a subdirectory.

My feature I'd love would be the ability to, in Windows Explorer, rt-click a file in that Dropbox folder and "send to:an email address". Rather than make an email with the file as an attachment though, it would make an email with a codified, temporary-within-timespan hyperlink to download that file from Dropbox's cloud. They get the email, they click the link, and they get immediate-no-website download of the linked file. That's what I'd love to see.