I've worked at several venues and Stub Hub can presenta problem. The same problems that affect any secondary market seller. What happens is people get the print at home tickets and copy them and sell the duplicates. Whichever of the tickets gets scanned in first gets entry to the venue all others do not. The same happens with the regular card stock ticket, people get them mailed to them, report them stolen (which voids the barcode) and have replacement tickets e-mailed to them which they use to enter the venue and the people who bought the tickets are refused.
The only good thing is that Stub Hub does have a ticket guarantee, meaning they'll refund you if you are turned away from the event, but you should know that there's a possibility that you'll be turned away at the door and miss whatever event you're trying to see.