Sometimes the user wants to change the MySite Link text to something else like "My World". In that case, you can do that by making changes to the MySiteLink.ascx file. This MySiteLink.ascx file is located at
C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\CONTROLTEMPLATES
Add visible="false"
Now, finally to change the Mysite text add the following line with the text that you want to display. Here, i want to display "Hello".