Dual Boot on XPS 15
Solution 1:
You have to turn off Intel Smart Response (switch to AHCI), to even get it to boot from dvd on one of these machines.
You need to turn off "Rapid start" technology or suspend will resume automatically in Ubuntu, and use up the battery.
Installation is mostly like any other computer, it runs 13.10 just fine. You can manually make a system partition on the SSD, and a home directory on the hard drive during the setup.
See also: https://wiki.ubuntu.com/HardwareSupport/Machines/Laptops/Dell/XPS/L521X#preview
It looks like the only no-go is the Bluetooth, at least in Kernel 3.11 until the drivers improve.
Update - I have since updated to 14.04 and bluetooth and everything works.
Solution 2:
Some more links. Not just precision model as XPS is similar.
http://en.community.dell.com/techcenter/b/techcenter/archive/2013/11/14/ubuntu-on-the-precision-m3800.aspx
Installing Ubuntu Alongside a Pre-Installed Windows with UEFI
https://help.ubuntu.com/community/Boot-Repair
Some that are mainly Windows users turn the Intel SRT back on after install. Others that use Ubuntu more leave SRT off and install / (root) into the SSD and all data or /home partitions on the hard drive. With the larger SSD, it may only be using part for the SRT and you can still have / on the SSD.