Robert Fripp (with Brian Eno) invented "Frippertronics" in the early 1970's by creating long delay tape loops for improvisation using two REVOX reel-to-reel tape recorders. He basically invented what we call looping for guitarists. Search YouTube for Frippertronics and you'll see some pretty interesting examples, from guitarists using digital delays, and some using tape delays.
It looks like the built-in looper can do this type of thing, so I'll be diving into the manual this weekend.