Since their release we've been buying Dell D820's for our developers. Overall feedback is very positive - a particular favourite seems to be the high res 1920 by 1200 screens. We've been buying the systems with 2GB of RAM, but recently had a requirement for a VMware demonstration machine so bit the bullet and specced one with the full 4GB, despite that nearly doubling the cost.
Unfortunately whilst the BIOS reports 4GB RAM as being installed, it shows only 3GB as available, the other 1GB being "reserved for use by the system". I couldn't find anything online about this but after consultation with Dell tech support it transpires that it's a problem with the A03 BIOS which apparently will be fixed in the A04 release scheduled for later this week.