If you are a software developer, you might know how hard it is to keep users running the most up to date versions of your software. WIndows is (in)famous for making users run Software Update all the time or bugging you to update with those silly message bubbles that will not go away.
The OSX text editor TextMate has solved this solution in a novel way, use RSS enclosures.
Like many other apps it has an Automatically check for updates but it also has the Download in the background option. In a nutshell this option will watch an RSS and when a new enclosure is added it will prompt you to update and can even do the update for you.
You might also notice that there is a option box for Watching what version you want. I have selected the Cutting-Edge but minor updates and major updates are also available.
So if getting users to upgrade is a problem with you, you should try using a RSS feed to help push the updates out to them.