I can't tell you how many legal secretaries I've tried to convince to stop hitting the space bar twice. I use full margin justification for my legal contracts and documents and adding two spaces after a sentence can leave too much white space between sentences. I remember taking typing in high school and being taught the two space bar rule after each sentence -- but that was on a manual typewriter.
For this and other great posts on contract drafting be sure to check out Adams Drafting, a great lawyer niche blog on contract drafting. I've been a regular RSS reader for a number of months.
Thanks to Alaina Crislip for pointing me to this post.