I did upgrade my Mac Mini from 3.5 to 3.7 last night, and all went well.
That is after I figured out how to actually do the update. I must admit I dont use my Mac Mini much these days, so I tend to forget how to this between each update.
So I go to http://www.morphos-team.net/installation and read the instructions for Mac Mini.

Mac mini:

- Turn on the Mac mini.

- In order to eject a previously inserted disc from your optical drive, press and hold your left mouse button during the reboot or power on process.
Insert the MorphOS CD immediately while holding the 'C' key.

- If the mini doesn't boot MorphOS or it has already booted another operating system, reboot and press and hold the 'C' key immediately after the welcome chime. Alternatively you can press and hold the Alt key to get to the mini's boot menu.

- MorphOS will now start booting. Once it is done booting, follow the on screen
instructions.

At this point I have already the CD in the slot, since I did use MacOS to download and burn the update image. So I press and hold 'C' while rebooting.
Then it apears to boot from the CD and I get the language choice menu and when I continue I get to the message that my boot.image is to old, and I am instructed to to the open firmware prompt and type: boot /pci/cd
I did try that, but only get an error message "load size to small" or something like that. At this point I was a bit frustrated, finding that both the on-screen instruction and the online installation notes seem to be wrong.
At the end I did the thing that worked, and of course it was as simple as holding Alt during boot and select the CD media for booting.

The Alt method is described as an alternative method in the installation instructions, but I did not catch this at first because it is written to be the solution if you cant boot MorphOS or if it already have booted another operatins system, and I did not feel that did apply for my situation.

I do have my Mac Mini set up with MorphOS/MacOSX 10.5.8 dual boot. Is this the reason that the instructions I get on-screen or online gets confusing?
If this is general for any MacMini setup, I wish they could update their instruction so its more clear how to do the update.

On the positive side, I just discovered that now for the first time the in-built wlan works on my MorphOS. Very good work! Now I can finally put my wlan bridge to rest.