I have unfortunately been having to commute to work and I have never had a problem unless the plane is oversold and multiple people are listed for the jumpseat ahead of me. There are 2 points as far as dress that I was told about when I started this 121 gig a few months ago, and both refer to being in full uniform. 1) TSA may/may not give you a hard time about the 3oz. BS if you are not in uniform. I have always been in uniform and never been given any scrutiny. 2) Jumpseating in the actual jumpseat (cockpit) requires you to be in the CASS system (my employer is) and you need to be in full uniform to actually occupy the seat. In the back it doesnt matter, but up front I have been told from the start that it does. I have heard of exemptions for sim instructors that must have line observations- but all pilots must be in full uniform. It has happened a couple times now that the flight was "wide open" but I ended up in the cockpit while others were left behind due to misconnects or cancelled flights changing the load count. Hope it helps, I may be wrong- I go hub to hub at the moment and the only flights are NW and 9E.