The only thing that annoyed me for a while was that the cursor keys don’t match the direction.
In Landscape mode, Up arrow moves the cursor left, instead of up… Why? Because Opera Mini thinks the arrow keys are oriented correctly when the phone is in Portrait mode. So when you switch to Landscape mode, it rotates the arrows too, so Up arrow moves Left, Right arrow moves Up, Down arrow moves Right and Left arrow moves

But I finally found a solution! Instead of setting Opera Mini to natively Portrait, we set it to natively Landscape. Then the arrow key orientation matches the default orientation and rotation works logically, albeit “Landscape mode” now engages Portrait orientation.

Add/change the following code in the JAD:
LGE-MIDlet-TargetLCD-Height: 240
LGE-MIDlet-TargetLCD-Width: 400
LGE-MIDlet-Height: 240
LGE-MIDlet-Width: 400
MIDlet-Screen-Mode: Landscape
MIDlet-Touch-Support: true
Navi-Key-Hidden: true

This will make Opera Mini default to Landscape mode, so do NOT enable Landscape mode in the Preferences, this will put it in Portrait.
The arrow keys will match the direction (Up arrow moves cursor up).

The only apparent side-effect, is that switching Opera Mini to Landscape mode puts it in Portrait mode, but upside-down with respect to the phone, so you’ll be holding your phone upside-down if you’re reading in portrait orientation. The arrow keys will still match the orientation, though (so the Left arrow moves the cursor down the page as you would expect, since the Left arrow is now facing down).

The same change works well for Google Maps and GMail. Still wish Google would sign the GMail app. Don’t have anything else loaded to mess with at the moment.