I leave mine oc'd and on 24/7 with restarts for software only...I think restarts are hard so in case every time you want to run faster you need to bootinto the bios to change it I wouldn't do it....If it is truly stable you should be fine...use sort of recommended or what has worked well vcore settings and you should be fine....
With an intel p4 system...northwood don't go over 1.7v actual at idle....ddr ram don't go over 2.8v max....use agp/pci lock to avoid any stress on pci and agp cards, as well as drives...
With amds I don't know the recommend safe range on xps, tbreds and the new bartons, but I hear 1.85v alot as a good stopping point...soulkeeper likes 2v but he burns them like I burn toast in the new toaster...