Not to make your decision any harder, but I just wanted to say that the D70 can create great pictures right out of the camera. Due to me being lazy and because I used Photoshop for a living I really don't like spending hours at work using Photoshop only to spend hours at home using Photoshop for my pictures. What this means is that I try to get my pictures correct straight from the camera and then adjust it in Photoshop when necessary. But this does mean that you have to adjust your D70 settings and not use the default auto settings. Nikon's default settings are pretty tame and conservative in my opinion.
As voodo mentioned you can load custom tone curves, but you can also increase color saturation and change the color hue in camera. It's kind of like using different film for different results, but the difference is that you change it back and forth with a few clicks of a button with the D70. Actually, I've been too lazy to load a custom curve but I've been content with what I can achieve from Nikon's settings. You just have to experiment and choose the setting that works for you. Of course, that doesn't help you much because you won't know if you like the custom settings until you've tried them. All I'm saying is that, at least for me, it is possible to get great pictures straight from the camera if that's important to you.
If you are a person who likes to post edit or doesn't mind post editing then I say look more at the features and functions you like. What's nice is that no matter which you choose they both use Nikon F mount lenses so if you do decide to go with the other then you wouldn't have wasted money on lenses. This is also nice way into the future when you decide to upgrade because you'll be able to choose between a Nikon or Fuji body to see which is better at the time. I don't know much about the Fuji S2 Pro so I can't really give you my impression but I've heard it's a good camera.
I have, however, read about the future Fuji S3 Pro camera which sounds like such a great camera. It has a greater dynamic range so you don't blow out highlights as much when trying to take pictures with a lot of contrast like sunsets. It also has settings to mimic film like Velvia. The price hasn't been announced yet so it may not be affordable by most. Sorry I didn't want to add another camera to your decision, but I thought I might as well mention it if you are willing to pay that much for the S2 Pro. The S2 Pro was never a choice for me because of the price.
My only major complaint about the D70 is it's small viewfinder. Even if you don't use manual focus, a larger viewfinder helps with things like DOF preview and all around detail composition. The Canon 300D is about the same size. You have to get a Nikon D100 or Canon 10D for a larger viewfinder. I believe the S2 Pro has a larger viewfinder but I'm not completely sure.