I gotta go with Limey on this one...especially for baby backs. I did get a rib rack thinking it would be nice for larger parties but the one time I tried it, the fact that the ribs curved over and sorta layed on each other prevented a bark. Then I doubled up on that by laying them out when I took the flat rack ribs out and smoking for another 30 minutes. They turned out dry from being in there too long.
So, if I just didn't do something right, please let me know how to make that rib rack useful. But unless I need to get more than 6 racks in my #2, I'll stick with laying them flat.