Interesting topic. I will generally move provided I get an aisle/window seat as I am pretty tall and therefore value my space (Always travel at the back and try for window seats on night flights).
I was really annoyed to hear that on her recent AMS-UIO flight to see me that my elderly mum was asked to move by passengers wanting to sit together... She ended up next to a Korean family who again asked her to move from the window to a middle seat so they could sit together and bless her, she refused. People like to take advantage!
Thankfully the chap she moved for in the first place had the good grace to reject the premium champagne meal I'd ordered for her once it came to her seat!