I checked a bag at IAD on 8/17 to ABQ via DEN and on 8/20 to LAS via ORD. No problem either time -- received my bag in good condition upon arrival. Both times, TSA had opened and inspected my bag.

BTW, unless you are 1K or UGS, be sure to use online check-in if you have bags. Even the 1P and 2P lines for checking bags at IAD were long on Sunday morning. There is a special line at United position 46 at IAD for checking bags -- IF YOU USED Easy Check-In Online. This line is very short and saves lots of time. It's open to any UA passenger, even non-elites.