is time to do clean up for the SharePoint environment , have 2 option i know we can do that. one is manual one is auto :P ha ha ha
Auto one you can setup at CA, Site use confirmation and deletion /_admin/applications.aspx . not sure how correct is it!! ha ha
but i prefer manual one.so use below query to check day last accessed , so we can guess is still used or not.
SELECT FullUrl AS 'Site URL', TimeCreated, DATEADD(d,
DayLastAccessed + 65536, CONVERT(datetime, '1/1/1899', 101)) AS
WHERE (DayLastAccessed <> 0) AND (FullUrl LIKE N'sites/%')
ORDER BY lastAccessDate