The used units are the 'old' 846 series design. The biggest problem with these units for SOHO is the noise. The use the old fans and - in addition to being 'non 80 plus' - the PSu has just a crazy loud fan in it. The $399 used chassis deal has been discussed over on AVS forum forum for quite a while now. If you read through those threads you'll see that most people either tolerate the noise or spend about $200 replacing fans and PSU to make them quiet enough for use. This makes the brand new $499 deal quite attractive.
Btw, Dba: I hate you. Or at least my wallet does...
Yea, that’s why the $499 unit is much more attractive for me as well. More efficient, newer design, etc. I also believe that some of the newer E5/E3 Xeon motherboards will not fit in the older chassis without some type of modification (i.e. dremeling). On the majority of supermicro's motherboard info pages it states "Important Chassis Note: To support the new generation Intel® Xeon® processor-based motherboards, Revision M chassis is recommended. Please talk to your sales representative for details.". Revision M came out with the E5/E3 xeon's, so the AMD servers are definately not rev M. I believe the heat sink mounting on the newer style Intel boards will not work with older chassis without some type of modification. You may want to mention this on your main page article.
I rembember on the HardForum someone complained about buying a new chasis and not having Rev M, Supermicro support stated that it is possible that with some modification it may work, but they would not divulge what those modifications were.
Now if there were cheap used motherboards out there that supported duel Xeon 5600 series chips we'd be in business.....