i wouldnt run it w\o a case. if you have any pets they might be intrigued by the new object and jump up on the table to investigate. even if you dont though its still dangerous, there is a reason cases are made out of metal, they need some type of grounding. testing them like that OK, running them full time, NOT ok.
they HAVE to have grounding, im pretty sure thats required by some type of code. well, at the very least manually ground the PSU\motherboard, i think thats the only things that are required to be grounded.