Ok, I've been battling this for ages and I'm a developer, this is what I have found.
I think there is still a problem on all configs, I'm not sure if it's an attempt to fix it in 10.8.3 of if no effort has been made to fix it, but the update has caused it to "move".
Anyway, those that think they has it fixed, try restarting a couple of times, you may find that the problem comes back!
Crashing. Flash seems to aggravate it and make it crash, note if you are running Flash when it crashes.
I can get it to work with rotated displays etc. but it takes a lot of messing around and I have to really think when I do it! Here is what I do (I think!), don't want to restart now cos I will have to swap cables etc.
If you have the "Black Screen Of Pointer Death" BSOPD, do this:
1. Shut down.
2. Unplug all monitors except for one in Slot 1, Port 1 that is in Landscape orientation. You can just move the cables at the Mac end if you are lucky - I am.
3. Power Up.
4. When it boots, and you are in the finder, open Display System Prefs.
5. Attach a new Monitor and wait for it to show up in Display Prefs.
6. If it's in the wrong orientation, click the gather windows button (in arrangement tab).
7. Set the Orientation of the monitor "gathered". This should now work ok, but if not, detach it and connect it to a different card, port. Eventually it should work - at least it has for me.
9. If you want all Portrait displays, do as above, but on the last one, switch the main menu screen to one of the displays already rotated.
10. Disconnect the remaining monitor (don't forget to shift display prefs into the (now) main screen.
11. Reconnect and change orientation as above.
This seems to work for me. I just can't imagine what Apple have done to stop this working and I can't possibly imagine why it would be difficult to fix. It worked fine prior to Lion, so surely a look at the differences in the source code between the two versions should highlight the problem? I just cannot believe this has gone unfixed for so long! What *is* going on at Apple?
All the Best
Currently I have a GTX670 installed into the Mac Pro driving 4 displays in portrait mode. While on the other hand, I have a GT120 sitting in the Mac Pro box. I'm looking to downgrade from the 670 since it's overkill just to drive multiple displays for working with documents. I'm about to buy another GT120 and it looks like I can drive 4 monitors off 2x GT120 cards, but since 10.8.3 still didn't fix this issue, I'm going to have to grab a Quad Monitor Stand to use them in Landscape mode.
Has anyone gotten 4 displays working in portrait mode working off multiple GT120 cards.
People are upgrading to a GTX6xx series from the GT120, while I'm downgrading from a GTX 670 to a GT120. There is nothing as awesome as the Apple boot screen and all the benefits you get with EFI.
Removed the 670 from my system since it's overkill for working with documents. I installed two GT120 cards and it seems like the issue is still there in 10.8.3. I'm now putting in a spare drive and installing Lion, just so I can get my displays to work.