Uh oh, the most unkillable meme in the OSGeo firmament is back, the XML map file. Even more unkillable than the "rasters in PostGIS" meme, the XML map file waits out the winters under the thick bark of .Net and Java programmers and blossoms every six months or so, until knocked back by the harsh frost of having-to-do-it-yourself and a Skeptical Development Community.
Me? I'm all for it. Check out my shopping list for today.
For me, it's all about human readability.