It's kind of funny because my SLR was a Pentax K-1000. I loved it to death, but it was auto-nothing (all it had was a through-the-lens light meter, which worked very well). So with the D70 I'm not so much learning how to use an SLR as how to use a
fancy SLR that actually does a lot of stuff for you.
A couple things about the D70 that you may already be aware of. First, when they say there's no delay turning it on, they are not exaggerating. Flip the switch take a picture (er, make that flip the switch, take the lens cap off, THEN take the picture). Also, the kit lens is pretty sweet - very sharp and a nice 28-105 range (35mm equivalent). Plus what I really like is the lens lets you manually override the focus on the fly at any time, without having to switch it to manual mode first. Not that you'd normally need that since the autofocus is very fast and seems quite accurate.
Of course if you've already invested in Nikon SLR lenses you're set because they intentionally used the same mount; unlike say the Canon Digital Rebel (which is still supposed to be a very nice camera).
The other thing that you're probably aware of is it'll really take advantage of a fast CF card. You can get a Lexar 80x 1G card for something like $169 at some places.
Oh, and the display screen on the back is just like the display screen on a fancy SLR - meaning you can't use it for framing/focussing like you could on a point-and-shoot digital. This didn't bother me because that was one of the things I HATE about digital cameras.

Give me a viewfinder with TTL focussing any day!