Rand Fishkin and Dharmesh Shah started Inbound.org - http://inbound.org/ - to be a similar community for online marketing. The links posted are pretty good, but so far the comments aren't adding a ton of value. Hopefully that will improve.
I don't think the comments will get better. It's a SEO site after all and you just need to take a look at sphinn.com to see what happens if you cater to a community of spammers and shadowy salesmen.
HN has a weird doublethink when it comes to SEO/marketing. We are all "hoorah!" startups, but how dare you try to make your site more appealing to a potential customer.
Sure, there are tons of scammers that use SEO...but there are tons of scammers in every field.