Just wanted to pass along a simplistic update checker that uses the GitHub Releases feature. If you use GitHub for managing your releases, this checker will look at the latest published release and compare to your current plugin version. It's pretty slick, because you can attach files to your release to avoid download issues with Dropbox or other services. It also gives you a nice place to manage the release notes & source files.
The updater file is located here. I may pull this out to a separate project at some point to make sharing easier, but that all depends on how often it is used and how much free time I have.
Currently, I'm using this in my Prowl Notify plugin for Indigo. Feel free to snag it and give it a shot in your plugin. It's pretty basic at this point, but it seems to work well. In the future, maybe it will even download the latest release for you
Please let me know if you end up using it or have any other questions / issues. Thanks!