WordPress 2.2 does not add trailing slashes to permalinks by default unlike older versions, resulting in duplicate copies of the same page indexed in search engines and hurting your ranking. A complete fix of this issue is discussed along with http to www redirection and ensuring only correct permalink url is shown even if other variation is used. Read Here : WordPress 2.2 Permalink Trailing Slash & Duplicate Pages Fix
Thank you I can't believe the WP team did this. I only noticed the missing slashes today - Google has noticed them too.