In many games the right click deselects/cancels an action.
For example left click on a fleet selects the fleet and then left click on a star moves the fleet.
If i want to select a star then first use right click to deselect the fleet and then left click on a star to select it.
That's what I had in mind.
Also in many software applications (not only games), scroll/pan is done by draging with right button pressed (not left) but i guess this could be configurable by users.
Really? I can't recall ever using right click to drag. Do you click and hold to drag, or click ones to start and once to stop? I'm used to google maps and similar, where left drag is used to pan, and most PDF viewers, where left drag pans.
A great improving of the interface would be to change the mouse cursor while moving over any active area (button, icon etc)
We generally highlight the thing under the cursor in these cases, rather than change the cursor itself.
Also a hourglass would be useful when the action is not done instantly (for example when selecting a star)
This is actually rather difficult to do with how the FreeOrion GUI is set up.
For comparison, another case I wanted to change was when starting a new game: It says "Generating Universe and AIs..." even after the AIs and Universe have been generated and downloaded, and it's just your local client processing the data and setting up the map screen. This is a problem because there were a few graphics system related crashes (typically inadequate OpenGL versions) that would cause crashes of the client, but the last thing the player saw was "Generating Universe and AIs" which seems like something happening on the server.
Unfortunately, the rendering system doesn't update until the main game logic is done processing whatever it's currently working on. In the case of processing an update from the server, after this is done the map immediately loads, hiding the text that would ideally have said something different, so there's no use in changing it after processing the update. The text can't be changed at the start of the processing of the update either, since the next render doesn't get done until after the processing, so the change would also never be seen.
Similarly with cursors, I'm semi-assuming that any updates wouldn't happen until the loading is done.
Better would be to load the art that slows down initial opens of the sidepanel in a background thread, but that's rather difficult to get set up properly, and not a high priority right now.