3
I don't think I've seen a site that uses clblocks or crblocks. Most just use the center block and put html formating in the content if they want columns.
Center uses the whole center area, cl and cr splits the center area in half so you can show content on each side.
so you can use:
|-leftcolumn-|-centerLcolumn-|-centerRcolumn-|-rightcolumn-|
or
|-leftcolumn-|-centerCcolumn-|-rightcolumn-|
which is what most sites use.
Take a look at the default theme.html, it'll show it better than I can explain
Rowd