get-mailbox  -identity twilliam | select name, @{n=”LastLoggedOnUser”;e={(Get-MailboxStatistics -id $_).LastLoggedOnUserAccount}}

Name               LastLoggedOnUser
——                ———————-
twilliam             CORP\twilliam

UPDATED:

Actually here is a better one :)

# ? = where-object
# ft -a = format-table -autosize

Get-MailboxStatistics -identity twilliam | ? {$_.objectclass -eq “mailbox”} | select DisplayName,Last* | ft -a

 DisplayName     LastLoggedOnUserAccount LastLogoffTime        LastLogonTime
———–     ———————– ————–        ————-
Williams, Tyler CORP\twilliam           11/26/2008 9:14:28 AM 11/26/2008 9:1…