Is there any advantage to using supercolumns (columnFamilyName[superColumnName[columnName[val]]]) instead of regular columns with concatenated keys (columnFamilyName[superColumnName@columnName[val]])?

When I designed my data model, I used supercolumns wherever I needed two levels of key depth - just because they were there, and I figured that they must be there for a reason.

Now I see that in 0.7 secondary indexes don't work on supercolumns or subcolumns (is that right?), which seems to me like a very serious limitation of supercolumn families.

It raises the question: Is there anything that supercolumn families are good for?

And here's a related question: Why can't Cassandra implement supercolumn families as regular column families, internally, and give you that functionality?