From http://weblogs.sqlteam.com/joew/archive/2007/08/31/60316.aspx, use these queries to check when statistics for indexes were last updated.
SELECT t.name AS Table_Name
,i.name AS Index_Name
,i.type_desc AS Index_Type
,STATS_DATE(i.object_id,i.index_id) AS Date_Updated
FROM sys.indexes i
JOIN sys.tables t
ON t.object_id = i.object_id
WHERE i.type > 0
ORDER BY t.name ASC ,i.type_desc ASC ,i.name ASC
SELECT name AS stats_name
,STATS_DATE(object_id, stats_id) AS statistics_update_date, *
FROM sys.stats
order by STATS_DATE(object_id, stats_id)