2
If you are using both Center-L & Center-R plus Center-C be aware that Center-L & Center-R always follow Center-C (and that weights have nothing to do with that precendence... at least that's been my experience.) So if you are trying to display any Center-C after a Center-L/R block you will loose out and find that the Center-C preceeds the L/R blocks.
That's only block-weight problem I've ever experienced.