The Windows Live team has chosen to discontinue the feature to leave notes within your friends’ Windows Live Profiles. Additionally, you cannot anymore send them Private Messages to other Windows Live users. Noticed by Microsoft MVP G. Winston Natoli, the corresponding web page now reads:
As opposed to the secure and rich-media messages that you can send with Hotmail, notes and private messages did not offer much functionality. So, these features were not used by many users, except for spammers, as usage analytics for the past time revealed.