This script will determine the active users and generate the report:

#!/bin/bash 
#Filename: active_users.sh 
#Description: Reporting tool to find out active users 

log=/var/log/wtmp 

if [[ -n $1 ]]; 
then 
  log=$1 
fi 

printf "%-4s %-10s %-10s %-6s %-8s\n" "Rank" "User" "Start" \ 
 "Logins" "Usage hours" 

last -f $log | head -n -2   > /tmp/ulog.$$ 

cat /tmp/ulog.$$ |  cut -d' ' -f1 | sort | uniq> /tmp/users.$$ 

( 
while read user; 
do 
  grep ^$user /tmp/ulog.$$ > /tmp/user.$$ 
  minutes=0 

  while read t  
  do 
    s=$(echo $t | awk -F: '{ print ($1 * 60) + $2 }') 
    let minutes=minutes+s 
  done< <(cat /tmp/user.$$ | awk '{ print $NF }' | tr -d ')(') 

  firstlog=$(tail -n 1 /tmp/user.$$ | awk '{ print $5,$6 }') 
  nlogins=$(cat /tmp/user.$$ | wc -l)  
  hours=$(echo "$minutes / 60.0" | bc) 

  printf "%-10s %-10s %-6s %-8s\n"  $user "$firstlog" $nlogins $hours 
done< /tmp/users.$$  

) | sort -nrk 4 | awk '{ printf("%-4s %s\n", NR, $0) }'  
rm /tmp/users.$$ /tmp/user.$$ /tmp/ulog.$$ 

The output resembles the following:

$ ./active_users.sh
Rank User       Start      Logins Usage hours
1    easyibaa   Dec 11     531    349
2    demoproj   Dec 10     350    230
3    kjayaram   Dec 9      213    55
4    cinenews   Dec 11     85     139
5    thebenga   Dec 10     54     35
6    gateway2   Dec 11     52     34
7    soft132    Dec 12     49     25
8    sarathla   Nov 1      45     29
9    gtsminis   Dec 11     41     26
10   agentcde   Dec 13     39     32