Useful unix command to find and replace text in many files

Here is a useful unix command I used today to find and replace text across multiple files and multiple directories.

find . -type f -exec sed -i "s/string1/string2/g" {} \;

This will replace all instances of string1 with string2.

Credit to Google and http://www.sb.fsu.edu/~soma/Proj/How-to/Search+Replace.pdf for helping me figure this out.