There is good news for Microsoft Hotmail users who found there mailboxes empty on 30 December 2010. Microsoft has posted on official blog post that all the emails have been restored. According to Microsoft the error occurred because of problem in mailbox load balancing between servers. Total of 17,355 user were affected by this problem and Microsoft team is further investigating the cause.
Though the mailboxes are restored this incident has raised a question of safety of data and credibility of Hotmail. I myself was not affected by the bug but I should suggest that you use a offline email clients like Mozilla Thunderbird or Outlook Express so that you have a offline backup for your important documents.