In the almost 10 years I was at Allegiant, I know of one person that went to Delta, and that was in either late 2007 or 2008, don't remember which. There could have been others, but that was the only one I personally know about.
I know there have been a bunch of us come to United, a bunch to Southwest and Alaska, a lot of the TWA furlough's have gone back to AA, a few that went to USAir prior to the merger with AA, and a couple to JetBlue and Spirit.
I know I've gotten a lot of phone calls from people wanting to know the secret to getting out.