I never look in my spam folder but looked today because of this discussion.
There were about 2000 messages in there from the past 30 days. Several were SEO proposals, a ton of messages from PR companies, but most were the spammy commercial messages for weight loss, payday loans, etc.
I did find one message that, in my opinion, should have been delivered to my inbox. It was a product information question for one of my ecommerce sites - about a month old.
I really like gmail because of the filtering abilities. I have lots of filters set up to trash messages based upon content, subject and sender.
My trash was full of invitations to connect on LinkedIn, reminders from LinkedIn, more crap from LinkedIn,
PR companies spammers that I have banned from my inbox, PR spam messages that were trashed because of filters, messages from a few people who used to bug me.
Yes, the filters are working great. I wish I could do the same with my telephone. If phone calls had subject lines my phone would ring at least 40% less often.