Im doing this with Steve Millers The Window. But anything will do, I
suppose. Impor a track, select all and copy to clipboard. Open a new window
of Audacity, paste, select all, then change the speed very very slightly (I
only changed it +0.07%). Select all, copy to clipboard, and flip back into
the original window. Creat a new stereo track, put the cursor at maybe 0.08
seconds, align the track with the cursor, then paste. The result is sort
of -- like a moving echo. As the two combined tracks slowly synchronize, it
sounds like theyre merging, or maybe that youre approaching a wall from
across a room, then moving away from the wall, as the slightly-faster track
pulls ahead of the other one. Anyone ever done that?

Heres one I did:
http://www.wikiupload.com/download_page.php?id=100764

At around 1:45 the two tracks converge and it sounds very cool.