Are you able to do full atomic transactions in Cassandra now? Like the ones described in the article:

    begin
        val1 = read(account1)
        val2 = read(account2)
        newVal1 = val1 - 100
        newVal2 = val2 + 100
        write(account1, newVal1)
        write(account2, newVal2)
    commit

Last time I checked this was not possible, only light compare-and-swap operations.