Earlier this year Gmail allowed new users to import contacts and messages from old email accounts to make switching easier. Today they've added that feature for everyone, meaning if you've got old email you'd love to import to Gmail, now you can.
Assuming you're already logged into your Gmail account, just point your browser to the Accounts and Import tab of your Gmail settings and click the Import mail and contacts button to get started. Then just follow along with the simple import wizard; enter your other email address, provide the password, and tell Gmail what you want to import, how you'd like it labelled, and whether or not you want to keep bringing in new mail for the next 30 days.
Mail and contact import for everyone [Official Gmail Blog]