I've had only one issue with the A4000T I use at work. The stock C= 040 processor card gave us no problems. Then we upgraded to a CS-PPC 060 card. That meant extra weight, different center of gravity, fan vibration, and a SCSI cable running to and from the board. The board simply would not stay properly seated in the long run.
There are solutions to this problem, but each one involves removing the mother board to replace the plastic stand-offs, or to add some straps. Eventually we just put the towner on its side and left it there. That ended our problems. As a bonus, two of the three monitors needed for our Toaster/Flyer fit nicely on the A4000SuperDeskTop.
Hopefully you will not encounter this problem. The A4000T has given great service to us otherwise. Wish I had one at home.
