I ordered an XPS 410n with Ubuntu on the day that they were announced. I set up the computer yesterday. Overall, it was extremely sweet-- a quiet machine, faster than my old machine, and the best Linux installation experience I've had since Redhat 5.2. (The first time is always special.)
Pictures are here: http://flickr.com/photos/pingswept/sets/72157600304529723/ Blog post is here: http://pingswept.org/2007/06/03/finally-booting-pre-installed-linux-on-an-oem-pc/
I would highly recommend buying an XPS 410n. Even Compiz is working without any advanced monkeying.
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And as an extra bonus, I emailed Mr. Shuttleworth to thank him for his efforts; he replied with a friendly note-- he's not just a visionary, but a decent person as well! I sent Ballmer emails throughout my years of compulsory patronage, and he wouldn't even throw a chair at me.