My cast iron skillet always has a black soot that comes out on the paper towel after I've cleaned and oiled it - is that normal?

Alton Brown recommended seasoning cast iron using just a bit of "hot fat" - whatever you've just cooked in it is fine - and a healthy scoop of kosher salt (inexpensive and very coarse).
Rub vigorously with a towel or rag (I have a dedicated dishcloth) until the salt is "dirty", then empty it out. If there are still bits of food stuck on (or your soot), rinse and repeat.
I've used this method ever since I found it, and it works well.

My guess is that you're not in any real trouble. A little black on a paper towel is okay. But if you find yourself getting to the point of thinking you should re-season the pan, then maybe you should also re-think your routine cleaning and get a little more aggressive. My well-maintained cast iron hasn't needed much attention in more than a generation. (Not that I'm some saint--I've done my share of re-seasoning.)

I would just put 2 cups or so of oil in and cook on low for awhile, be sure to watch it though. This always seems to fix that problem :)

Mine does the same thing. I believe that it's just the seasoning that you are working to create. As long as my CI works like non-stick and is smooth, I just keep cooking. Maybe once or twice a year, the surface becomes rough. That's when I re-season.