The American Scene web log allows comments. Their blogging software has a feature which only accepts comments after the writers have reviewed what they have written.
For those, like myself, who often find errors in our comments only after we have posted them, this feature provides a distinct advantage. I find that as I type, my thinking often outruns the signals going to my fingers, so I often find a word with the last letter of the word I had intended to type before it attached. Also, when I go back and change a sentence, I often leave a word that no longer belongs. Previewing my work beforehand sometimes saves me from looking foolish.