Well, OK, the title’s a little misleading, but here’s a very handy hint for anyone running Lion or later. It’s to do with moving files.
Though the Finder has, for a very long time, supported the copying and pasting of files from one folder to another, it has never allowed cut and paste. I could never fathom why something so simple wasn’t in there until I realised that, actually, there is a problem with implementing the concept cleanly: normally, when you cut things, they disappear. What happens if you cut a file but never paste it? Especially accidentally? (What happens on Windows? I forget…)
Still, this was an annoying omission, particularly if you’re used to Windows, or if you have a small display without much space for dragging things about.
Well, now you can do it. Instead of the normal cut & paste keystrokes (Cmd-X, Cmd-V) you do a copy and a kind of alternate paste (Cmd-C, Alt-Cmd-V). Intuitive? No. But I guess it makes a kind of sense.
Thanks to the excellent David Sparks for the hint.