Using the latest nightly available (r37469), when I go to me.com the user name and password that is saved in my keychain does not appear in the text areas as it does in Safari 3.1.2 apart of 10.5.5 However, it should be noted that if you click the login button you will in fact be sent to your mobileme mail as you should have evan though the fields are blank.
Created attachment 24348 [details]
Screenshot of issue...
It should also be noted that once the text boxes are clicked on as if you place the cursor, the text at that point will then autofill that box.
works now in latest nightly (r37698)