Shoot-em-ups are the thing, now. Nobody has the kind of time and patience required for serial killing anymore, and advances in forensics make the risk too high. Besides, it's too personal. Easier to just waltz into public and start spraying bullets. I don't mean to make light of it or whatnot. It's just an interesting shift in the trends of homicide.
Serial killers and spree shooters are very different creatures, mentally speaking. They're both killers, yes, but a serial killer wants that personal touch and has specific targets. A spree killer is just angry at whatever they're angry at -and they are patient. At first glance it may seem as if your day-to-day spree killer just picked up a firearm and went to town, but that's rarely the case. Most of the time they've been planning their 'day' for years.
According to the FBI, in the United States alone there are anywhere between 40-60 serial killers active at any one time (depending on which source you read, the numbers vary from 40 to 60). Serial killers don't get the publicity they used to because it's not so shocking anymore and they usual get caught pretty early on, but they're not dropping the knife and deciding to shoot up a building full of people instead -that's a whole other animal.