I decided to give the demo a go, and I've played it a couple times with Deon and a few others. Then I installed an addon that allows you to (in a somewhat hacky fashion) play as the infected.
Man, that's loads o' fun. Even though he's not exactly the most powerful, I've got a special place in my heart for the Jockey, just because he oozes personality.
And pus. He oozes pus too. But mostly personality.
I actually think it'd be fun to have a sort of mini-game, "The Steeple Chase". Four survivors without weapons, four jockeys. A racetrack. The survivors win by fighting their jockey and finishing last, the jockeys win by finishing first. An epic battle of wills between survivor and infected!
But maybe that's just because I happen to have a hell of a time riding people, and just want to do it more often.
Anyways, I noticed a few quirks. For instance, AI survivors will not shoot a boomer close-range because of their explosive bile. However, if you are a boomer and you've managed to lock yourself into close quarters with them, simply hit the attack button (not barf) and they'll shoot you before you can get a swipe off.
This can, of course, be completely circumvented by simply binding the "kill" command to a key and then hitting it at an appropriate time...
On the waterfront map, it's possible to load as an infected and run down to where the survivors are before their intro animations are over. This allows you to puke on all of them with impunity, causing a massive rush of infected to come barreling down the walkway. Again, loads of fun.
I've also had a couple instances where I'll line up a charger's rush just perfectly, where I crash into all of the survivors and then run off for quite a distance while still carrying one of them. In the time it takes everyone else to pick themselves up and run after me, I've been able to have all sorts of fun with my new little squishy-toy.
Also, AI survivors cheat. Like, bad. I've been shot through solid walls a couple times, and they don't seem to have any effect on the witch. I was playing a smoker and hiding behind a wandering witch, so they'd shoot her instead of me. One of them unloaded on me from about sixty feet away with a submachine gun. Killed me, left the witch standing and still just aimlessly dawdling. Dang.