The Exchange Management Console for Exchange 2007 or 2010 doesn’t have a reporting functionality. If you want to have a report on the mailboxes within your organization you will need to use the Exchange Management Shell.

When you want to report the mailbox size and the last logon time for all the mailboxes in your organization, you can use the following commandline.

get-mailbox -resultsize unlimited | Get-MailboxStatistics | sort -property lastlogontime -descending | ft displayname, alias, server, totalitemsize, storagelimitstatus, lastlogontime  >c:\export.csv

If you need more information in the outputfile, you can add properties to the command.