なにやら新機能が追加されたようです。
http://mail.google.com/mail/help/whatsnew_getmail.html
Just launched!
Get mail from other accounts
Now Gmail can check for the mail you receive at your other email accounts. You can retrieve your mail (new and old) from up to five other email accounts and have them all in Gmail. Then you can even create a customized 'From:' address, which lets you send messages from Gmail, but have them look like they were sent from another one of your email accounts. Please note that you can only retrieve mail from accounts that have POP3 access enabled. Learn moreThis feature is currently only enabled for a limited number of users. We're working on making it more available soon. Look for it in the 'Accounts' tab in Settings.
チェックするメールアドレスを追加できて、Fromを変更できるって事らしい。GmailがOE/Becky!などのメールクライアントと同等になるね。
JP版は使ってないので英語ですが。JP版でも使えるんだろうか。