I thought I had up to date backups with my TM...no errors in logs and showing hourly backups completed. However, I found out the hard way this is not true all the time. I had to reload my Mini at the recommendation of AppleCare because a failed removal of a Bootcamp partition was locking up the Mini upon restart. Well, SL was reloaded and I told it to restore data from my TM backup. Low and behold, the last date of "up to date" media was dated 3/5/10! So I lost over a week's mail, iCal appts, taxes!, financials, iTunes, etc.