When I started IntelliJ (9.0.1, community edition) today, it popped a dialog up with an option to download a "patch" to install 9.0.2 release.
I've clicked "Download Patch" before, but nothing ever happened, and I ended up resorting to a full install.
But today, I came across a comment that described how to apply the patch:
And it worked great for me.
Others on my team said their patches installed just fine. To be clear, I'm using the Community Edition, and it may only be an issue with that edition.