I'd avoid the E-500 due to the noise issues. Also, there is no
upgrade path with Olympus, nor is there a good selection of lenses.
With Nikon, you have huge availability of lenses, both new, used, and
third-party.

In the course of investigating the Nikon, upgrade path has been
something I've begun to explore. I've read posts about the d70(s) vs
d50. I'm not experienced enough with the high-end to properly assess
feature differences. That said, if I'm looking at the d50 w/ 18-70 vs
the d70 w/ 18-70 at a similar price should I be looking to the d70?

I'm going to take a spin over the local camera shop today to get a feel
for both of these models.