I needed to check this up with Grammar Girl again! 😉 And I wasn’t really surprised to read that the spelling of do’s and don’ts is inconsistent. Even style guides and usage books don’t appear to agree on the correct punctuation.
The Chicago Manual of Style and others recommend dos and don’ts. The Associated Press and others recommend do’s and don’ts. While Eats, Shoots & Leaves (on my bookshelf) recommends do’s and don’t’s.
Whichever version you choose, just be consistent!