Seriously, I'm in the market for a new laptop and there are still too many concerns relating to support for these devices... not just Dell but usually for whatever manufacturer I'm looking at. Once you start reading about people's experiences there are always issues - many of which have been discussed to death on HN.
Just because Dell claim that Linux is officially supported does not mean that it will be a smooth ride. I don't think that has changed much at all over the last few years? But perhaps this year is different.
Do you own this though? If you're using this new XPS model without power consumption issues, excellent wifi (wifi chips issues seem to always be the main downer), good mousepad behaviour? Perhaps it's finally not a problem? I will gladly lap up any positive news that you can give on this front.