I take the NY subway whenever the ride home from work is too long ( I work all over the city), my legs are too tired, or the weather is too bad. Whenever I have had to take the subway with my BF , I have folded it so that I don't take up too much real estate. A long bike, be it a folder or not, in the way of commuters is far more of an inconvenience than a folded one by my feet.
When I get out of the train, it takes me about 2 minutes to get the bike set up and ready to go, including putting the chain back on the front chain ring ( the greatest short fall of the BF). I don't fold it a lot, so I would imagine that if I did it often, the unfolding time would decrease by 50% or more.
Foldability combined with the fantastic ride of my Carusoe, makes me take the bike out far more than I would if I had either a crummy folder, or a full size non-folder.
Its going to rain today, probably pretty hard in the afternoon....... Think I'll ride to work.................