My main email is not GMail, but I forward it to a GMail account to get free spam filtering, free backup, and free search. I encourage everyone to do the same.
Like I recently had to turn off alias for made4men.no. srsly, signing me up for spam and not removing me from the spam list even after i unsubscribed. You can tell it's a swedish shop that just happens to own a Norwegian domain.
I actually had to do the opposite. I have a filter that catches all messages marked as spam and unmarks them as spam. VERY rarely there's a spam message caught in there. Much more often sth super important that just would have landed in spam if not for my genius spam filter.