For my beater I use a Kryptonite combination U-Lock and the sheldonbrown.com method. I usually am too lazy to lock my front wheel, but do take the seat post with me.
One of the mysteries of NYC bike theft is why it takes seconds sometimes for a bike to be stolen, and other times a desirable bike will be abandoned but chained to a pole and over the years be slowly dismantled until there is just a fairly desirable frame. After a few years of seeing one of these I cut the lock off and kept the chain.
You should also note that subway fare is $2.25 each way or $4.50 a trip. 200 days a year that is $900. So you can justify 2 or 3 beaters stolen a year just on the fare you save.
It is actually fairly rare for a beater to be stolen if it is ULocked with one of the better ulocks. If they are many times the rider did not lock the bike properly.