I've noticed that STEMM->SBD and back again has no transaction fees... and no transaction expiration. Sort of makes a bunch of pre-set micro-transactions staged up as buy/sell order possible for a semi-manual HST algorithm.
I've actually been having a fair amount of fun with it (with my measly $20 or so I'm playing with) over the last few weeks with how active the price changes have been. I wonder, how many others are taking advantage of this sort of movement and these features with much wider spreads of money?