I bought a 1420 preinstalled with Ubuntu 7.04 at the beginning of the summer.  I upgraded it to 8.04 and have just upgraded it to 8.10 release candidate yesterday.  Mostly it worked, but there were two major problems that I will describe with directions to the solution for those who come after me. 

1.  Intrepid includes the 177.80 nvidia driver.  This driver caused my fan to always be working at top speed.  The solution is to upgrade to the a09 BIOS - See this description for how to do this:  http://www.ubuntu-unleashed.com/2007/09/howto-easily-upgrade-dell-bios-in.html  - If upgrading the BIOS frightens you (and it probably should a little), you can also choose to use the 173.xx NVIDIA driver.  

2.  The webcam stopped working.  It was found and the light would come on, but I never saw any video.  Apparently the uvcvideo driver that is currently shipping in the intrepid RC kernel is broken.  You have to replace it with one compiled from hand.  See instructions here:   https://bugs.launchpad.net/ubuntu/+source/linux/+bug/287888 - I hope this bug is fixed by the final release.  

Any other problems I encountered were minor. 

-Jack