the energy demand of the disks would be twice : the inner side of the laptop would get hotter, thus leading, in some circumstances, to less reliable HW (I have a 3 yrs old laptop which has half broken connectivity because it was too hot before I could fix it)….

Another solution would be a laptop
without
classical HD inside it (ex: the OLPC and the eeeeeeeePC) and the classical (magnetic, now very cheap if new, with big capacity and known life expectancy) disks outside it, where they can get as hot as they want without damaging anything else : modern BIOSs can boot on the USB, and many Linux can be installed on such disks or on USB pendrives ( TinyMe for PCLOS, Arch made one this month or gave an how-to, Mandriva has done it for years -began in 2004-, and I may forget hundred of them….) .
This solution ,as many outside disks outside the laptop can make him less hot, can increase the laptop’s life expectancy, but need being plugged to reliable main power supply…