It doesn't matter if you hide the email address, it still exists. And if you have one of those custom facebook URL's, it is easy to guess the email address. It's the name in your URL @facebook.com.
Before the email address was optional, now it is not. You have it whether you want it or not, plan to use it or not, hide it or not. And you don't get to choose one that is different than the name you already use for facbook's custom URL.
And it will be so easy for the spammers to figure it out, even if you remove it from your profile.
If you have ever made a comment on a company's fan page, ever liked something popular, friended anyone else that has, they will easily find you to spam you.
Just imagine the notifications for every spam message, mixed in with the ones for private messages from friends and family.
This is going to be a disaster for Facebook with a lot of people closing their accounts and going elsewhere. Just a matter of time, now.