They still do it--happens with me every now and then. I check my bag in about 3:30 ahead of time, then fly a single-connection with a three hour or so layover (I prefer longer layovers), and arrive at my destination to find out that my bags arrived ahead of me.

As far as security rules go, "the bag must be on the same plane as the passenger" only applies to international flights. For domestic flights, while obviously it'll raise eyebrows if you request that your bag be put on an earlier flight, if the airline decides to do it themselves that's up to them and perfectly fine.