Ok, so everyone probably already knows this one. Still, it’s almost as invaluable as Continuous Grab to me. When hovering the mouse over any value, colour or text field, just hit Ctrl+C to copy the value and then Ctrl+V when hovering over another field to paste it there.
One could argue about how Blender is missing all sorts of industry standard features like particle meshing and alembic cache support, but honestly these tiny usability features are what I love most about Blender (apart from the great community of course ;) ). Though that’s not to say I wouldn’t like to have particle meshing and alembic cache support ;)