I have both a D70 and a D70s. The only differences that I can actually see are (1) larger LCD on the "s", and (2) longer battery life for the "s".
I did do the firmware upgrade on the D70 last summer, which supposedly narrows the difference between the two cameras. Also, the battery recall netted me an EN-EL3e battery, which has the same mAh rating as the EN-EL3a which came with the "s".
Thus the only difference that I see, as a user, is the slightly larger LCD display. There may be other, more subtle, differences that I don't notice in actual use. I think the "s" is supposed to focus faster, but after the firmware upgrade I haven't noticed any differences.