If you ever dealt with Emoticons in your content you may find a difference regarding the path that is used to reference the icon images depending if you use Domino 9.0.1 Fixpack 1 or 2. I noticed that for a while but now I examined that a little closer:
If you create content in a richtext control and use an Emoticon (aka a Smiley) you may get broken links to that image resource that resides on the server.
The path that is used using the server environment with FP1 installed is this path:
But if you are creating your content on a server using FP2 you will receive this one
Both paths are computed via the richtext control aka the CKEditor that ships with each of the versions - and there are more differences though.
So beware to mix up content creation or considider to use the fixpacks in all of your environments when creating new content. This will fail though with data that has already been created as the paths aren't valid anymore in an FP2 environment.
Please IBM, fix this Fixpack asap - and don't forget to address the iOS8 upgrade problems though I'm not affected with it but others are.