do u like to take picture? if yes, pick the n8. both are different in alot of ways.
N8's os is Symbian Anna, upgradable to Belle. 710's is Window Phone 7.5.
N8 has the best camera on a smartphone, 12 megapixel with a carl zeiss lens.
N8 had much fewer apps in its Ovi store, compared to 710's marketplace.
there are much more difference like processor, but i dont think they matter