I'm not a big movie buff, generally movies are contrary to the whole point of this blog... but this is an exception.
I watched this movie once before, back in 2009 at "they mayors" (a hostel in new york) while hiking the AT. This weekend I watched it again with Jess, and being aware of such things now I was struck by the costuming and accuracy.
Jeremiah Johnson is the most physically accurate movie I'm aware of for bushcraft skills of the mountain man era. If you watch their clothing carefully it really is the furs and buckskin that it should be. The clothing also has to be at least near warm enough as apparently they had very few onsite amenities during the shoot :P. Jeremiah's clothing is even sewn in a European style while the various Indian* tribes wear clothes in Indian styles. Watch him start the fire using rocks... I don't know if he actually started it, but his technique sure looks legit to me. It's very similar to a method I learned for using star Iron Pyrite.
I don't know much about the filming of the movie, but I didn't see any gross inaccuracies in the Indian villages and such. I'm suspicious that they may have actually had the real tribes in the movie directly. I'm no Crow specialist though I admit.
Anyway, If you're into bush-craft, or just enjoy historically accurate movies about the mountain man era, I highly recommend it for a rainy day. It will make you want to get out there again as soon as you can.
After much Linux hacking I got things working so I could watch it off amazon.com (if you want tips on that, I now have too much experience, feel free to ask).
(Full disclosure: I'm posting this because I think it's legitimately interesting, but I will get a tiny kickback if you use the link above)
BTW... My understanding is that Sons of Jeremiah Johnson is nothing like the original with terrible inconsistencies, "bad" people, etc.
* I try and use the term American Indian since reading 1491, where the author points out that based on his (fairly extensive) experience most tribes in the U.S. prefer this term.