Here's what I put on the post-- thought I'd repeat it here for those who don't want to wade thru all of the people bashing Matt Maroon. :-)
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Hehe. The obvious solution for this is to, uh, submit articles to News.YC.
FWIW, a good percentage of my posts (which often appear on YC News) have to do with SEO ( http://www.tonywright.com/category/seo/ ).
(Disclosure: I am a YC08 Founder)
I think it's a "devil you know" issue, to some degree-- I actually offered to help some other YC founders with their SEO plans and didn't get a lot of uptake- people prefer to tackle the problems they understand.
Another issue (and this might be controversial) is that maybe SEO doesn't matter a damn bit for most early stage startups... At least in the very early stages (which is what most people tend to write about).
I always look at startups as a bucket with holes in it. You can focus on increasing the flow of water into the bucket (SEO, viral, PR, marketing) or you can work on patching the holes in the bucket (adding value, improving product/market fit, improving the "lower" part of your funnel). With time being the most scarce resource in a startup, any time you spend improving "flow" takes away from "patching the bucket".
If you've got a great "bucket" (a product people freakin' LOVE and love to talk about), all of the "flow" tasks get a lot easier. If you've got a mediocre"bucket" with lots of holes, great "flow" isn't going to help make patching the bucket easier.
So (as a guy who has built and sold 2 businesses and the third is looking pretty darn good), I'd recommend ignoring a concerted SEO effort in favor of making your product better (if you have to make a choice). Ideally, you're funded and you don't HAVE to make a choice (but most startups do).