For some reason, Google also marks "Google Alerts" notifications as spam. They contain spammy search results, but the email comes from Google.
At least they are consequent in not white-listing their own services :)
Gmail also marks messages from gmail or other google services as spam. Gmail also marks all legitimate mails from Paypal as spam (phishing). I use several email addresses and google accounts, but in the end I forward most mails into the same gmail box. Their spam filters cannot handle the concept of forwarded mail correctly.