I'm interested to hear interesting uses for Dropbox accounts outside of the normal occasional file share. Do you keep your entire working documents directory in Dropbox? In what unique ways are you using the service or have you heard of others using the service?
I use a development environment and language called LiveCode (http://www.runrev.com) dropbox allows me to keep my plugins and libraries for the IDE at a common place. This way, all my LiveCode instances in multiple machines in different offices are always in sync. Not unlike putting your .emacs and site-lisp in there or something similar.
I also use it as a poor man processing queue for some of my personal tools where a machine will place a file in a specific folder and another worker machine will notice and pick it up and further process it saving it to a different place where a third machine will do its job, like an assembly line (and the machines are in different countries), quite easy to setup for very simple tasks
I use dropbox and LAMP together to 'distribute' small projects.
Basically I install dropbox on a linux box, and use apache's mod_vhost_alias to automatically map incoming requests to the correct folder. Most of the time I use sqlite as DB storage so the file stays in the dropbox folder.
When I want to put changes online I just copy/paste the files. Of course this is no way of working when you have bigger sites or sites that have a lot of db changes, but when you get there you better find more suitable hosting then the one I have anyway.
I like this way because the dropbox folder is synced with my netbook and macbook as well, so my setup is quite portable!
A small trick: Because Dropbox can only watch and sync one directory, and because I don't want to move all my stuff in that directory, I create symbolic links to the stuff I want sync'ed in the Dropbox directory.
Man i wish I could give you 10 upvotes, you have just solved my only issue with Dropbox. I have like 4 machines that I work on regularly and this has now allowed me to sync all those config files you cannot easily move e.g. iTunes including the iPhone backups, Chromium user data.
Install Dropbox and symlink to your server's webroot, share a project folder for your application code. Makes your live 'deployment' instant as file->save.
I keep a huge bash_profile with lots of aliases in dropbox and then load it on the real .bash_profile of my computers with: ". ~/Dropbox/Configs/bash_profile"
I actually keep most of my files in Dropbox, which lets me keep everything the same between my desktop and netbook. I add the appropriate Dropbox folder to my Windows 7 libraries, and that makes it feel the same as saving documents in the normal Documents folder. Then, I keep portable apps in a Dropbox folder so they're synced between machines as well. Works great for me!
I recently used Dropbox to collaborate on an appengine python project with a friend and loved it. Since python is interpreted we didnt have too many issues with working on the same file at the same time (no compilation errors).
My Dropbox folder has replaced my documents folder entirely. I also save preferences and sync files within Dropbox, so I can run the same program (say, 1Password) from multiple computers with exactly the same data.
I also use it as a poor man processing queue for some of my personal tools where a machine will place a file in a specific folder and another worker machine will notice and pick it up and further process it saving it to a different place where a third machine will do its job, like an assembly line (and the machines are in different countries), quite easy to setup for very simple tasks