How does sleep/suspend work? That was always the biggest hangup for me. Although, it's been almost a decade since I last tried. However, a colleague's Dell running Ubuntu was a nightmare. Not sure if it was the model or how he had it set up though.
Sleep and suspend just work. Battery life is good - typically 5-7 hours. Before this I had no problems with a Thinkpad and even on a MacBook Air (2012).
Maybe I'm just so used to Linux now that I don't notice problems since I've been on it since 1998-ish except for a short stint on OS X.
Dell support is terrible so I can't recommend the XPS. When I had a problem with the battery they wouldn't replace it under warranty since I was not in the country where I bought it, which is total BS.