http://itunes.apple.com/us/app/wiki-offline-wikipedia-experience/id378348813?mt=8
I'm not affiliated with these guys.
I've been wanting something like this for a while but I was PLANNING on building "collections" of documents related to specific areas of interest.
However, at 3.5G downloading ALL of wikipedia isn't TOO bad.
This way when I'm in the wilderness I can read ANY page I want.
Also, the impact on first aid is important here to. If you get some WEIRD medical symptoms when in the back country you have a pretty verbose mechanism of information to help figure it out.
So far I've been carrying my iphone for music so I might carry it for wikipedia too :-P

