What criteria does XM use on what songs they play during this? It seems like it's pretty extensive. I thought it may be every song that hit the Top 40???? I missed the 40's. I really like Big Band music. The 60's and 70's are right down my alley too as this was the time I was growing up. This is really neat thing XM does. I heard it about a year and half ago when they did it last.