I'm running an M3800 with Mint Linux 17.3. I can squeeze 2 hours out of the battery if I really need to; suspend/hibernate is currently completely broken, requiring that I cold boot the machine each time I open the lid; bluetooth has never worked properly, even after extracting the proprietary firmware from the Windows drivers.

And this is on a machine that shipped from Dell with Ubuntu 14.04 installed, so supposedly all the hardware is open-source friendly.