Changing the user associated with a computer en masse?

Well, on the machine itself, you can tell the JAMF Binary to run a recon, and specify the user who 'owns' the machine. In our case, we specify the user's username and an LDAP server to pull their info from:

jamf recon -endUsername auser -ldapServerID 1

Our environment names machines using their owner's username, so updating everyone was a simple matter of getting the computer name, trimming it with sed, and then using that to set the owner. If the mac has a non-standard name, we flag it via a Smart Group scoped to a ARD Field we check for. It's probably ugly, but it works:

#!/bin/sh
#First, get the computer name from JAMF
COMPUTERNAME=`jamf getcomputername`
echo "JAMF Reports $COMPUTERNAME as the name of this Mac"

#Clear ARD Fields
jamf setARDFields -target / -1 Hello

#Check That $COMPUTERNAME is a standard name that fits our filter
#Filter: -mac or -macX, then for -MAC or -MACX, then for TVs, then assume oddball.
if [[ $COMPUTERNAME == *-mac<* ]] || [[ $COMPUTERNAME == *-mac[0-9]<* ]];
    then
        #Trim string to username only
        OWNER=`echo $COMPUTERNAME | sed -e 's|^.*>(.*)-.*$|1|'`

        #Echo result to STDOUT
        echo "My Scrying Script tells me $OWNER owns this Mac..."

        #Set Scried owner as the Machine owner, via recon
        jamf recon -endUsername $OWNER -ldapServerID 1

        #Finally, echo some output so that we know what happened
        echo "...so I set $OWNER as the owner of this Mac."

    elif [[ $COMPUTERNAME == *-MAC<* ]] || [[ $COMPUTERNAME == *-MAC[0-9]<* ]];
        then
            #Trim string to username only
            OWNER=`echo $COMPUTERNAME | sed -e 's|^.*>(.*)-.*$|1|'`

            #Echo result to STDOUT
            echo "My Scrying Script tells me $OWNER owns this Mac..."

            #Set Scried owner as the Machine owner, via recon
            jamf recon -endUsername $OWNER -ldapServerID 1

            #Finally, echo some output so that we know what happened
            echo "...so I set $OWNER as the owner of this Mac."       

    elif [[ $COMPUTERNAME == *-tv<* ]] || [[ $COMPUTERNAME == *-tv[0-9]<* ]];
        then
            #Machine is a Tableau TV - ignore!
            echo "This machine is a TV. User should be set manually in JSS to maintainer of the TV."
            jamf setARDFields -target / -1 TV
            jamf recon

    else
        #The Machine has a non-standard name - don't change the owner!
        echo "$COMPUTERNAME is an oddity - writing Oddball to ARD Field 1. Cursed be ye!"

        #Set ARD Field 1 to Oddball, which adds machine to a SmartGroup, and Recon that to the JSS
        jamf setARDFields -target / -1 Oddball
        jamf recon
fi
exit 0

I have a script that runs at each login. It captures the "current" user and fills it under "Location -> Username" and also so we can view the location history trails to see who have used the laptop in the past.

#!/bin/sh

#
#
#

/usr/sbin/jamf recon -endUsername $3