In Reproducing Vim help as a fully cross-referenced PDF, Nathan Grigg talks about a project he embarked on to create a cross-referenced PDF of Vim's documentation:
It's a long story, but for the last six months, I have been using Vim as my primary text editor. As I began to use Vim more often, I was frustrated by the lack of a tutorial that went beyond the basics. I finally found what I was looking for in Steve Losh's Learn Vimscript the Hard Way, which is an excellent introduction to Vim's power features. I also discovered the real reason there are no advanced tutorials, which is that everything you need to know is contained in Vim's help files.
One of the goals was an iPad-friendly PDF. He used Latex, and eventually ended up with an 11-megabyte, 2500-page PDF, which actually reads quite nicely.
There are different versions for iPad, A4, and US letter, so you should be able to view it comfortably on a wide range of devices. I'm always interested in discovering new ways to read technical documentation on the go, because I commute quite a lot, so I think I'll stick this on a Kindle and see how it goes.