One of the most interesting changes, for me at least, was the change of the phrase "white and delightsome" in the BOM to "pure and delightsome."
It used to be that the book of Mormon discussed the fact quite clearly that dark skin marked those who rebelled in the pre-existence against God. And, conversion and purity could cause people's skin color to change to a lighter hue. This was justification for denying the priesthood to people of dark skin until the 1970s. The book of Mormon was then changed to reflect changing doctrine in 1981.
Here's a great resource on the changes in the BOM. Many are quite substantive, including the one I've highlighted above.
http://www.irr.org/mit/changingscrips.html