My final take-away was that if Dell can get their act together with the XPS 15's reliability, it could be an acceptable alternative on a price/performance basis.
Reliability was a concern for me too when I experimented with the XPS 15, but the fact of the matter is that everything is easily user-serviceable. So when 1TB starts to look pathetic, you can easily swap in a 4TB drive, etc. It looks to me like you can't even replace the SSD on any of the new 15" macs (or if someone figures out how, it is going to be a nightmare.) This limits its useful life, no matter how reliable it is.