As a follow-up post on duplicate content on WordPress blogs – here’s an additional tip.

You can stop the search engines from indexing duplicate pages such as monthly/daily archives by using the following code snippet:

if(is_home() || is_single() || is_page() || is_category() || is_tag())
{
       echo ‘<meta name=”robots” content=”index,follow” />’;
}
else
{
        echo ‘<meta name=”robots” content=”noindex,follow” />’;
}

You can add or remove arguments in line 1 to include or exclude pages form being indexed.

The code should be inserted into the <head> section of header.php.