Key Index/Key Slices

[Mark]

Keys are indexed in Cassandra but are they ordered? If so, how?
Do Key Slices work like Range Slices for columns.. ie I can give a start 
and end range? It seems like if they are not ordered (which I think is 
true) then performing KeyRanges would be somewhat inefficient or at 
least not as efficient as a slicing across columns. Is the case?

ColumnFamilyFoo: {
  "a" : {},
  "b" : {},
  "c" : {}
}

ColumnFamilyBar: {
   "all" : {
      "a" : --
      "b" : --
      "c" : --
   }
}

Is doing a KeySlice "a" through "c" on ColumnFamilyFoo pretty much the 
same thing as doing a RangeSlice "a" through "c" on ColumnFamilyBar on 
key "all"?

Thanks for the explanation