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If you want to use logical markup to indicate document changes, there are the <ins> and <del> tags. The advantage of these tags is that they hold semantic meaning, and also support a timestamp attribute. On the other hand, I believe they're not as widely supported by older browsers as the physical tags, mentioned above.
Nick
Are you saying that the <em> and <strong> tags are being deprecated as well? I thought they were replacements for the <b> and <i> tags because they were semantically (instead of stylistically) relevant. Also, for that reason, I believe that they have meaning to screen readers as well, which CSS styles would not.