In my mind, it raises the bigger question around ownership of a user's profile--not just in Facebook, but any social media site, or CRM (customer relationship management) system, or well, anywhere. If you want to collect my information so that you can keep in touch with me, market to me, and eventually sell me something, wouldn't you want ME to be the one informing you when changes need to be made to my profile?
And if you want to add extra value to the service you're providing me, say by giving me a complimentary email address, don't you think you'd better give me the option on whether to accept that offer, or maybe just an option on whether it is listed as a primary or secondary email address on my profile?
Most recently, Facebook has had to hurry up and react to complaints that mobile users whose device's contacts synchronize with Facebook are seeing existing email addresses for friends/family being replaced with the @facebook.com addresses--a major convenience for many. And, hardly perceived as a value-add! Here's a great video tutorial on how to restore your address book after Facebook messed it up.
What did you do when you learned that your primary email address listed on Facebook was now an @facebook.com address?
I wonder what happens if you set your Facebook notifications to be sent to your Facebook email address?!