I'm typing this listening to the Jesu / Eluvium split LP which is a much treasured piece of vinyl of mine. First side is Jesu, second half is Eluvium. I think this is a great idea because the two bands are in some ways similar and yet obvioulsy very different. I bought it for the Jesu songs but it's the Eluvium stuff that is now closer to my heart.
So... why doesn't this happen more often? I know Bright Eyes have done a few but... it seems like a great way for indie labels to get a bit of cross pollination going in their fanbases.