Biggest downside I saw was you are paying a 50% markup in Dell or Lenovo... But I guess no more pricey than Apple. (But no apple retina screens)
I had a System 76 laptop around 2010, and it was great except for the battery life. I'll probably try another one at some point.
My advice: if you want a solid development platform, System76 is the way to go (and will cost half as much). If you care more about a nice retina screen and dont mind mac os, stick with a mbp.
Though to be fair I primarially do data analysis and not heavy application development.
I imagine it is even better than the ones that we currently use, which are over four years old and still do everything we need them to do in stride.
Caveat: Almost none of us run these machines with Ubuntu. Debian or Mint are common, but so is Arch.
Never had any problem running Linux on it (I use Linux Mint). The quality is OK. The keyboard wasn't great, and the battery deteriorate really quickly. To elaborate, at the beginning I could get 5 hours, but after 2 or 3 years I had to replace it (Customer service was great btw).
I can assume that the newest generation fixed a lot of issue (based on photos the keyboard now looks much better). I would definitely buy a new one the day they decide to finally offer a 13''.
Dell Precision 17 7000's can be ordered with Ubuntu 12.04 LTS. They come standard with three year next business day onsite warranties.
http://www.dell.com/us/business/p/precision-m7710-workstatio...