Whenever our mac users get a new message the notes client jumps to focus immediately. This is very frustrating and there appears to be no way to change this behavior. Even turning off mail alerts does not stop it.
Subject: Workarounds
That’s what I experienced, too.
Even if Notes is not the only application who does it (e. g. iTunes does it, too) it’s still very annoying.
I found two workarounds (well, kind of):
a) Hide Lotus Notes 8.5 Beta 2 (using CMD-H)
b) Minimize it (using the yellow ball icon in the window title)
Both work for me: Notes no longer steals the focus.
Subject: Better inn 8.5 release; but starting up is a mess
While writing this post (on a Mac), I received a Notes mail and Notes didn’t steal focus this time; just the bouncing icon on the doc 
However, while starts up Notes (which takes a while), it seems to steal focus for every GUI-detail it loads, making it hard to do anything else before it’s done. Anoying if you’r only starting Notes for the mails sake, while reading news on the web for example…
Subject: This has been fixed for GA.
Just to set expectations – we haven’t fixed 100% of the focus stealing cases, but it is much improved.
Subject: Any improvement VERY welcome!
This is my major beef with Notes 8.5. I am constantly seeing Notes pop up when I’m typing away in some other application, and it’s driving me insane! I hope you don’t stop trying to get to 100% resolution of this issue…