Here's a bash snippet to show who's been checking in code to a mercurial repository:
hg log | sed -n "s/user: *//p" | sort | uniq -c | sort -rn
This prints something like:
262 Pablo
108 juanita
23 carlos
23 Maria Castano <maria@gmail.com>
21 Juan Hernandez (hernandez@gmail.com)
17 psalamanca
13 chico
7 Maria Castano <maria.castano@yahoo.com>
1 paco
Update: For an alternative measure try the churn extension.