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I have not come across any "enterprise" commenting system either, that surprises me because it should exist. I am looking for a system that caters for really large websites. Disqus and Facebook are good but from a SEO perspective they have no value.

Your point is also valid Yousaf, however it's up to automated algorithms to determine what's valid, what's not, what's acceptable use and what's not.  That's the concern.  If you feel truly confident that your use could in no way be perceived algorithmically as being a problem, then feel free to proceed. Personally I live in the world of best practices and recommend to clients that they avoid such potential pitfalls whenever possible.  Of course, that does limit their ability to make the most out of web technology, but that is sometimes a price that has to be paid when such risks could harm their revenue stream.

That's a nice list you've got there, I particularly liked the disclaimer about public relations at the top of the page ;-). We're putting something together that's similar, but coming at it from a PR agency perspective rather than straight linkbuilding for SEO. Well, the wedding's over so this may not help the OP directly, but could be useful for others: For tech clients we use sourcewire regularly (and find it works very well) For cheap, releases that still give half-decent links and get picked up by google news, we often use www.journalism.co.uk (which I didn't see on your list and costs about £30 for the basic service) As a (slightly) amusing aside, we put an April Fool's blog post up about being appointed the PR agency for the royal wedding - would you believe we actually got a couple of enquiries from journalists asking us for information about it! I dread to think how many more enquiries we would have got had we used a wire.