I've got the Dell XPS 13 Developer Edition laptop, of which I am a big fan. My touchpad works in 17.10 without a problem, but when I boot into 18.04, I get bad behaviour. I can move the pointer, but it's jerky, and just stops following my touchpad movement.
It works fine when I boot to a 17.10 USB key. Using a USB mouse also works fine. The problem occurs when I have a USB mouse connected or not.
I get the same behaviour when I start an Xorg session or a Wayland session, so my guess is that the problem is at a lower level, like the kernel.