Hi Eric,
You can hide columns in the aircraft list by using File > Preferences > General and unticking the columns you don't want to see. You can't change the order of the columns, but you can change the sort order of what is in those columns by clicking on the column title - Mode S, Flight ID, Registration etc.
Mode S is not so widely used in the USA, although this is planned to change over the coming years when full ADS-B will probably be introduced (I have a couple of aviation articles from the US Aviation Week I must scan and post here).
Also, you need to take into account the time difference for the USA. At the moment, 6.00pm UK time, I can see loads of traffic up the east coast of the USA, quite a bit around LAX about 8 around SFO.