I have no idea. IMO this Dell touchpad will still be finicky and frustrating to use compared to the Mac. It's all in the drivers and software.
Microsoft has worked with Intel to improve the touchpad experience from the software side for Windows 8.1. We don't know yet how this will affect the XPS 15 at launch, or over time as the software becomes compatible with more hardware. The touchpad in this video is easily as responsive as that on a Macbook Pro, so there is some hope.
http://www.youtube.com/watch?v=j0QOIWoTJYw
I will admit that the touchpad is probably my biggest concern about the XPS 15. It's the main reason I won't buy one until Anand or Notebookcheck does a review of it. With the rMBP an excellent touchpad is guaranteed. Hopefully Microsoft will be able to bring quality to their OEMs' touchpads. This has been a major selling point for Apple laptops for a long time.
The XPS 13 specification lists the touchpad resolution as 250 cpi. While there isn't necessarily a direct correlation a direct correlation between cpi and dpi it still suggests that the hardware on the XPS 15 might be much better.