One of the great things about vim is that even if you use it as your regular editor (I use MacVim), you tend to learn something new every time you read a new article. Today I learned about the '.' command.
= will also indent any selection you have automagically. gg=G will do your whole document, and V[selection]= will give you a selection range to indent. < and > are nice as well for indenting specific amounts in the left or right direction.
Also, old discussion on same article: http://news.ycombinator.com/item?id=151637